| Message ID | 20241107055817.489795-2-sourabhjain@linux.ibm.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | fb90dca828b6070709093934c6dec56489a2d91d |
| Headers | show |
| Series | [v2,1/2] powerpc/fadump: allocate memory for additional parameters early | expand |
| Context | Check | Description |
|---|---|---|
| snowpatch_ozlabs/github-powerpc_selftests | success | Successfully ran 8 jobs. |
| snowpatch_ozlabs/github-powerpc_ppctests | success | Successfully ran 8 jobs. |
| snowpatch_ozlabs/github-powerpc_kernel_qemu | success | Successfully ran 21 jobs. |
| snowpatch_ozlabs/github-powerpc_sparse | success | Successfully ran 4 jobs. |
| snowpatch_ozlabs/github-powerpc_clang | success | Successfully ran 5 jobs. |
Sourabh Jain <sourabhjain@linux.ibm.com> writes: > The param area is a memory region where the kernel places additional > command-line arguments for fadump kernel. Currently, the param memory > area is reserved in fadump kernel if it is above boot_mem_top. However, > it should be reserved if it is below boot_mem_top because the fadump > kernel already reserves memory from boot_mem_top to the end of DRAM. did you mean s/reserves/preserves ? > > Currently, there is no impact from not reserving param memory if it is > below boot_mem_top, as it is not used after the early boot phase of the > fadump kernel. However, if this changes in the future, it could lead to > issues in the fadump kernel. This will only affect Hash and not radix correct? Because for radix your param_area is somewhere within [memblock_end_of_DRAM() / 2, memblock_end_of_DRAM()] which is anyway above boot_mem_top so it is anyway preserved as is... ... On second thoughts since param_area during normal kernel boot anyway comes from memblock now. And irrespective of where it falls (above or below boot_mem_top), we anyway append the bootargs to that. So we don't really preserve the original contents :) right? So why not just always call for memblock_reserve() on param_area during capture kernel run? Thoughts? > > Fixes: 3416c9daa6b1 ("powerpc/fadump: pass additional parameters when fadump is active") > Cc: Mahesh Salgaonkar <mahesh@linux.ibm.com> > Cc: Michael Ellerman <mpe@ellerman.id.au> > Acked-by: Hari Bathini <hbathini@linux.ibm.com> > Signed-off-by: Sourabh Jain <sourabhjain@linux.ibm.com> > --- > > Changelog: > > Since v1: https://lore.kernel.org/all/20241104083528.99520-1-sourabhjain@linux.ibm.com/ > - Include Fixes and Acked-by tag in the commit message > - No functional changes > > --- > arch/powerpc/kernel/fadump.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/powerpc/kernel/fadump.c b/arch/powerpc/kernel/fadump.c > index 3a2863307863..3f3674060164 100644 > --- a/arch/powerpc/kernel/fadump.c > +++ b/arch/powerpc/kernel/fadump.c > @@ -143,7 +143,7 @@ void __init fadump_append_bootargs(void) > if (!fw_dump.dump_active || !fw_dump.param_area_supported || !fw_dump.param_area) > return; > > - if (fw_dump.param_area >= fw_dump.boot_mem_top) { > + if (fw_dump.param_area < fw_dump.boot_mem_top) { > if (memblock_reserve(fw_dump.param_area, COMMAND_LINE_SIZE)) { > pr_warn("WARNING: Can't use additional parameters area!\n"); > fw_dump.param_area = 0; > -- > 2.46.2
Hello Ritesh, On 12/11/24 11:51, Ritesh Harjani (IBM) wrote: > Sourabh Jain <sourabhjain@linux.ibm.com> writes: > >> The param area is a memory region where the kernel places additional >> command-line arguments for fadump kernel. Currently, the param memory >> area is reserved in fadump kernel if it is above boot_mem_top. However, >> it should be reserved if it is below boot_mem_top because the fadump >> kernel already reserves memory from boot_mem_top to the end of DRAM. > did you mean s/reserves/preserves ? Yeah, preserves is better. > >> Currently, there is no impact from not reserving param memory if it is >> below boot_mem_top, as it is not used after the early boot phase of the >> fadump kernel. However, if this changes in the future, it could lead to >> issues in the fadump kernel. > This will only affect Hash and not radix correct? Because for radix your > param_area is somewhere within [memblock_end_of_DRAM() / 2, memblock_end_of_DRAM()] > which is anyway above boot_mem_top so it is anyway preserved as is... Yes. > > ... On second thoughts since param_area during normal kernel boot anyway > comes from memblock now. And irrespective of where it falls (above or below > boot_mem_top), we anyway append the bootargs to that. So we don't really > preserve the original contents :) right? Sorry I didn't get it. We append strings from param_area to boot_command_line not the other way. > So why not just always call for > memblock_reserve() on param_area during capture kernel run? > > Thoughts? Yes, there is no harm in calling memblock_reserve regardless of whether param_area is below or above boot_mem_top. However, calling it when param_area is higher than boot_mem_top is redundant, as we know fadump preserves memory from boot_mem_top to the end of DRAM during early boot. According to the memblock documentation, when reserving memory regions, the new regions can overlap with existing ones, but I don't see any advantage in calling memblock_reserve for param_area if it falls above boot_mem_top. Regardless, I don’t have a strong opinion. If you think we should call memblock_reserve regardless of where param_area is placed, I can do that. Please let me know your opinion. Sourabh Jain > >> Fixes: 3416c9daa6b1 ("powerpc/fadump: pass additional parameters when fadump is active") >> Cc: Mahesh Salgaonkar <mahesh@linux.ibm.com> >> Cc: Michael Ellerman <mpe@ellerman.id.au> >> Acked-by: Hari Bathini <hbathini@linux.ibm.com> >> Signed-off-by: Sourabh Jain <sourabhjain@linux.ibm.com> >> --- >> >> Changelog: >> >> Since v1: https://lore.kernel.org/all/20241104083528.99520-1-sourabhjain@linux.ibm.com/ >> - Include Fixes and Acked-by tag in the commit message >> - No functional changes >> >> --- >> arch/powerpc/kernel/fadump.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/arch/powerpc/kernel/fadump.c b/arch/powerpc/kernel/fadump.c >> index 3a2863307863..3f3674060164 100644 >> --- a/arch/powerpc/kernel/fadump.c >> +++ b/arch/powerpc/kernel/fadump.c >> @@ -143,7 +143,7 @@ void __init fadump_append_bootargs(void) >> if (!fw_dump.dump_active || !fw_dump.param_area_supported || !fw_dump.param_area) >> return; >> >> - if (fw_dump.param_area >= fw_dump.boot_mem_top) { >> + if (fw_dump.param_area < fw_dump.boot_mem_top) { >> if (memblock_reserve(fw_dump.param_area, COMMAND_LINE_SIZE)) { >> pr_warn("WARNING: Can't use additional parameters area!\n"); >> fw_dump.param_area = 0; >> -- >> 2.46.2
Sourabh Jain <sourabhjain@linux.ibm.com> writes: > Hello Ritesh, > > > On 12/11/24 11:51, Ritesh Harjani (IBM) wrote: >> Sourabh Jain <sourabhjain@linux.ibm.com> writes: >> >>> The param area is a memory region where the kernel places additional >>> command-line arguments for fadump kernel. Currently, the param memory >>> area is reserved in fadump kernel if it is above boot_mem_top. However, >>> it should be reserved if it is below boot_mem_top because the fadump >>> kernel already reserves memory from boot_mem_top to the end of DRAM. >> did you mean s/reserves/preserves ? > > Yeah, preserves is better. > >> >>> Currently, there is no impact from not reserving param memory if it is >>> below boot_mem_top, as it is not used after the early boot phase of the >>> fadump kernel. However, if this changes in the future, it could lead to >>> issues in the fadump kernel. >> This will only affect Hash and not radix correct? Because for radix your >> param_area is somewhere within [memblock_end_of_DRAM() / 2, memblock_end_of_DRAM()] >> which is anyway above boot_mem_top so it is anyway preserved as is... > > Yes. > >> >> ... On second thoughts since param_area during normal kernel boot anyway >> comes from memblock now. And irrespective of where it falls (above or below >> boot_mem_top), we anyway append the bootargs to that. So we don't really >> preserve the original contents :) right? > > Sorry I didn't get it. We append strings from param_area to > boot_command_line > not the other way. > > Right. My bad. >> So why not just always call for >> memblock_reserve() on param_area during capture kernel run? >> >> Thoughts? > > Yes, there is no harm in calling memblock_reserve regardless of whether > param_area > is below or above boot_mem_top. However, calling it when param_area is > higher than > boot_mem_top is redundant, as we know fadump preserves memory from > boot_mem_top > to the end of DRAM during early boot. So if we don't reserve the param_area then the kernel may use it for some other purposes once memory is released to buddy, right. But I guess, given we anyway copied the param_area in fadump_append_bootargs() during early boot to cmdline (before parse_early_param()), we anyway don't need it for later, right? In that case we don't need for Hash too (i.e when param_area falls under boot_mem_top), right? Since we anyway copied the param_area before parse_early_param() in fadump_append_bootargs. So what is the point in calling memblock_reserve() on that? Maybe I am missing something, can you please help explain. -ritesh > > According to the memblock documentation, when reserving memory regions, > the new > regions can overlap with existing ones, but I don't see any advantage in > calling memblock_reserve > for param_area if it falls above boot_mem_top. > > Regardless, I don’t have a strong opinion. If you think we should call > memblock_reserve regardless > of where param_area is placed, I can do that. Please let me know your > opinion. > > Sourabh Jain > > > >> >>> Fixes: 3416c9daa6b1 ("powerpc/fadump: pass additional parameters when fadump is active") >>> Cc: Mahesh Salgaonkar <mahesh@linux.ibm.com> >>> Cc: Michael Ellerman <mpe@ellerman.id.au> >>> Acked-by: Hari Bathini <hbathini@linux.ibm.com> >>> Signed-off-by: Sourabh Jain <sourabhjain@linux.ibm.com> >>> --- >>> >>> Changelog: >>> >>> Since v1: https://lore.kernel.org/all/20241104083528.99520-1-sourabhjain@linux.ibm.com/ >>> - Include Fixes and Acked-by tag in the commit message >>> - No functional changes >>> >>> --- >>> arch/powerpc/kernel/fadump.c | 2 +- >>> 1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/arch/powerpc/kernel/fadump.c b/arch/powerpc/kernel/fadump.c >>> index 3a2863307863..3f3674060164 100644 >>> --- a/arch/powerpc/kernel/fadump.c >>> +++ b/arch/powerpc/kernel/fadump.c >>> @@ -143,7 +143,7 @@ void __init fadump_append_bootargs(void) >>> if (!fw_dump.dump_active || !fw_dump.param_area_supported || !fw_dump.param_area) >>> return; >>> >>> - if (fw_dump.param_area >= fw_dump.boot_mem_top) { >>> + if (fw_dump.param_area < fw_dump.boot_mem_top) { >>> if (memblock_reserve(fw_dump.param_area, COMMAND_LINE_SIZE)) { >>> pr_warn("WARNING: Can't use additional parameters area!\n"); >>> fw_dump.param_area = 0; >>> -- >>> 2.46.2
Ritesh Harjani (IBM) <ritesh.list@gmail.com> writes: > Sourabh Jain <sourabhjain@linux.ibm.com> writes: > >> Hello Ritesh, >> >> >> On 12/11/24 11:51, Ritesh Harjani (IBM) wrote: >>> Sourabh Jain <sourabhjain@linux.ibm.com> writes: >>> >>>> The param area is a memory region where the kernel places additional >>>> command-line arguments for fadump kernel. Currently, the param memory >>>> area is reserved in fadump kernel if it is above boot_mem_top. However, >>>> it should be reserved if it is below boot_mem_top because the fadump >>>> kernel already reserves memory from boot_mem_top to the end of DRAM. >>> did you mean s/reserves/preserves ? >> >> Yeah, preserves is better. >> >>> >>>> Currently, there is no impact from not reserving param memory if it is >>>> below boot_mem_top, as it is not used after the early boot phase of the >>>> fadump kernel. However, if this changes in the future, it could lead to >>>> issues in the fadump kernel. >>> This will only affect Hash and not radix correct? Because for radix your >>> param_area is somewhere within [memblock_end_of_DRAM() / 2, memblock_end_of_DRAM()] >>> which is anyway above boot_mem_top so it is anyway preserved as is... >> >> Yes. >> >>> >>> ... On second thoughts since param_area during normal kernel boot anyway >>> comes from memblock now. And irrespective of where it falls (above or below >>> boot_mem_top), we anyway append the bootargs to that. So we don't really >>> preserve the original contents :) right? >> >> Sorry I didn't get it. We append strings from param_area to >> boot_command_line >> not the other way. >> >> > > Right. My bad. > >>> So why not just always call for >>> memblock_reserve() on param_area during capture kernel run? >>> >>> Thoughts? >> >> Yes, there is no harm in calling memblock_reserve regardless of whether >> param_area >> is below or above boot_mem_top. However, calling it when param_area is >> higher than >> boot_mem_top is redundant, as we know fadump preserves memory from >> boot_mem_top >> to the end of DRAM during early boot. > > So if we don't reserve the param_area then the kernel may use it for > some other purposes once memory is released to buddy, right. But I guess, > given we anyway copied the param_area in fadump_append_bootargs() during > early boot to cmdline (before parse_early_param()), we anyway don't need > it for later, right? > > In that case we don't need for Hash too (i.e when param_area falls under > boot_mem_top), right? Since we anyway copied the param_area before > parse_early_param() in fadump_append_bootargs. So what is the point in > calling memblock_reserve() on that? Maybe I am missing something, can > you please help explain. > Ok. I think I got it now. You did mention in the changelog - "Currently, there is no impact from not reserving param memory if it is below boot_mem_top, as it is not used after the early boot phase of the fadump kernel. However, if this changes in the future, it could lead to issues in the fadump kernel." So it is not an issue now, since the param area is not used after the contents is copied over. So I think today we anyway don't need to call memblock_reserve() on the param area - but if we are making it future proof then we might as well just call memblock_reserve() on param_area irrespective because otherwise once the kernel starts up it might re-use that area for other purposes. So isn't it better to reserve for fadump use of the param_area for either during early boot or during late kernel boot phase of the capture kernel? But now that I understand I don't have a strong opinion too (since it is just future proofing). But I would prefer the safer approach of doing memblock_reserve() always for param_area. So I will leave it upto you and others. >> >> According to the memblock documentation, when reserving memory regions, >> the new >> regions can overlap with existing ones, but I don't see any advantage in >> calling memblock_reserve >> for param_area if it falls above boot_mem_top. >> >> Regardless, I don’t have a strong opinion. If you think we should call >> memblock_reserve regardless >> of where param_area is placed, I can do that. Please let me know your >> opinion. >> >> Sourabh Jain >> >> >> >>> >>>> Fixes: 3416c9daa6b1 ("powerpc/fadump: pass additional parameters when fadump is active") Not really IIUC, this is not really a fix but a future proofing of if fadump ever tries to use param_area later during early boot or during late kernel boot. -ritesh >>>> Cc: Mahesh Salgaonkar <mahesh@linux.ibm.com> >>>> Cc: Michael Ellerman <mpe@ellerman.id.au> >>>> Acked-by: Hari Bathini <hbathini@linux.ibm.com> >>>> Signed-off-by: Sourabh Jain <sourabhjain@linux.ibm.com> >>>> --- >>>> >>>> Changelog: >>>> >>>> Since v1: https://lore.kernel.org/all/20241104083528.99520-1-sourabhjain@linux.ibm.com/ >>>> - Include Fixes and Acked-by tag in the commit message >>>> - No functional changes >>>> >>>> --- >>>> arch/powerpc/kernel/fadump.c | 2 +- >>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>> >>>> diff --git a/arch/powerpc/kernel/fadump.c b/arch/powerpc/kernel/fadump.c >>>> index 3a2863307863..3f3674060164 100644 >>>> --- a/arch/powerpc/kernel/fadump.c >>>> +++ b/arch/powerpc/kernel/fadump.c >>>> @@ -143,7 +143,7 @@ void __init fadump_append_bootargs(void) >>>> if (!fw_dump.dump_active || !fw_dump.param_area_supported || !fw_dump.param_area) >>>> return; >>>> >>>> - if (fw_dump.param_area >= fw_dump.boot_mem_top) { >>>> + if (fw_dump.param_area < fw_dump.boot_mem_top) { >>>> if (memblock_reserve(fw_dump.param_area, COMMAND_LINE_SIZE)) { >>>> pr_warn("WARNING: Can't use additional parameters area!\n"); >>>> fw_dump.param_area = 0; >>>> -- >>>> 2.46.2
Hello Ritesh, On 12/11/24 17:23, Ritesh Harjani (IBM) wrote: > Ritesh Harjani (IBM) <ritesh.list@gmail.com> writes: > >> Sourabh Jain <sourabhjain@linux.ibm.com> writes: >> >>> Hello Ritesh, >>> >>> >>> On 12/11/24 11:51, Ritesh Harjani (IBM) wrote: >>>> Sourabh Jain <sourabhjain@linux.ibm.com> writes: >>>> >>>>> The param area is a memory region where the kernel places additional >>>>> command-line arguments for fadump kernel. Currently, the param memory >>>>> area is reserved in fadump kernel if it is above boot_mem_top. However, >>>>> it should be reserved if it is below boot_mem_top because the fadump >>>>> kernel already reserves memory from boot_mem_top to the end of DRAM. >>>> did you mean s/reserves/preserves ? >>> Yeah, preserves is better. >>> >>>>> Currently, there is no impact from not reserving param memory if it is >>>>> below boot_mem_top, as it is not used after the early boot phase of the >>>>> fadump kernel. However, if this changes in the future, it could lead to >>>>> issues in the fadump kernel. >>>> This will only affect Hash and not radix correct? Because for radix your >>>> param_area is somewhere within [memblock_end_of_DRAM() / 2, memblock_end_of_DRAM()] >>>> which is anyway above boot_mem_top so it is anyway preserved as is... >>> Yes. >>> >>>> ... On second thoughts since param_area during normal kernel boot anyway >>>> comes from memblock now. And irrespective of where it falls (above or below >>>> boot_mem_top), we anyway append the bootargs to that. So we don't really >>>> preserve the original contents :) right? >>> Sorry I didn't get it. We append strings from param_area to >>> boot_command_line >>> not the other way. >>> >>> >> Right. My bad. >> >>>> So why not just always call for >>>> memblock_reserve() on param_area during capture kernel run? >>>> >>>> Thoughts? >>> Yes, there is no harm in calling memblock_reserve regardless of whether >>> param_area >>> is below or above boot_mem_top. However, calling it when param_area is >>> higher than >>> boot_mem_top is redundant, as we know fadump preserves memory from >>> boot_mem_top >>> to the end of DRAM during early boot. >> So if we don't reserve the param_area then the kernel may use it for >> some other purposes once memory is released to buddy, right. But I guess, >> given we anyway copied the param_area in fadump_append_bootargs() during >> early boot to cmdline (before parse_early_param()), we anyway don't need >> it for later, right? >> >> In that case we don't need for Hash too (i.e when param_area falls under >> boot_mem_top), right? Since we anyway copied the param_area before >> parse_early_param() in fadump_append_bootargs. So what is the point in >> calling memblock_reserve() on that? Maybe I am missing something, can >> you please help explain. >> > Ok. I think I got it now. You did mention in the changelog - > > "Currently, there is no impact from not reserving param memory if it is > below boot_mem_top, as it is not used after the early boot phase of the > fadump kernel. However, if this changes in the future, it could lead to > issues in the fadump kernel." > > > So it is not an issue now, since the param area is not used after the > contents is copied over. So I think today we anyway don't need to call > memblock_reserve() on the param area - but if we are making it future > proof then we might as well just call memblock_reserve() on param_area > irrespective because otherwise once the kernel starts up it might re-use > that area for other purposes. So isn't it better to reserve for fadump > use of the param_area for either during early boot or during late kernel > boot phase of the capture kernel? Seems like there is some confusion. Here is the full picture with the current patch: First kernel boot: Reserve param_area during early boot and let it remain reserved. First kernel crashed Fadump/second kernel boot fadump_reserve_mem() does memblock_reserve() from boot_mem_top to end_of_dram(). This covers param_area if it is above boot_mem_top. fadump_setup_param_area() does memblock_reserve() for param_area only if it falls below boot_mem_top. This ensures it is covered if param_area falls below boot_mem_top. This way, we make sure that param_area is preserved during the fadump kernel's early boot in both cases. Note: fadump_reserve_mem() is executed before fadump_setup_param_area(). IIUC, you are suggesting doing memblock_reserve() for param_area in fadump_setup_param_area() regardless of its location. If we do this, memblock_reserve() will be called twice for the case where it falls above boot_mem_top. I agree there is no harm in doing so, but do we have to? Again, I don't have a strong opinion on this but just wanted to put things forward to make sure we are on the same page. Let me know your opinion. Thanks, Sourabh Jain >>> According to the memblock documentation, when reserving memory regions, >>> the new >>> regions can overlap with existing ones, but I don't see any advantage in >>> calling memblock_reserve >>> for param_area if it falls above boot_mem_top. >>> >>> Regardless, I don’t have a strong opinion. If you think we should call >>> memblock_reserve regardless >>> of where param_area is placed, I can do that. Please let me know your >>> opinion. >>> >>> Sourabh Jain >>> >>> >>> >>>>> Fixes: 3416c9daa6b1 ("powerpc/fadump: pass additional parameters when fadump is active") > Not really IIUC, this is not really a fix but a future proofing of if > fadump ever tries to use param_area later during early boot or during > late kernel boot. The reason I put the Fixes tags because we mistakenly put the wrong condition there. The intention was to reserve memory if it below boot_mem_top. But yes if see this patch as future proofing the Fixes tag can be avoided. - Sourabh Jain > >>>>> Cc: Mahesh Salgaonkar <mahesh@linux.ibm.com> >>>>> Cc: Michael Ellerman <mpe@ellerman.id.au> >>>>> Acked-by: Hari Bathini <hbathini@linux.ibm.com> >>>>> Signed-off-by: Sourabh Jain <sourabhjain@linux.ibm.com> >>>>> --- >>>>> >>>>> Changelog: >>>>> >>>>> Since v1: https://lore.kernel.org/all/20241104083528.99520-1-sourabhjain@linux.ibm.com/ >>>>> - Include Fixes and Acked-by tag in the commit message >>>>> - No functional changes >>>>> >>>>> --- >>>>> arch/powerpc/kernel/fadump.c | 2 +- >>>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>>> >>>>> diff --git a/arch/powerpc/kernel/fadump.c b/arch/powerpc/kernel/fadump.c >>>>> index 3a2863307863..3f3674060164 100644 >>>>> --- a/arch/powerpc/kernel/fadump.c >>>>> +++ b/arch/powerpc/kernel/fadump.c >>>>> @@ -143,7 +143,7 @@ void __init fadump_append_bootargs(void) >>>>> if (!fw_dump.dump_active || !fw_dump.param_area_supported || !fw_dump.param_area) >>>>> return; >>>>> >>>>> - if (fw_dump.param_area >= fw_dump.boot_mem_top) { >>>>> + if (fw_dump.param_area < fw_dump.boot_mem_top) { >>>>> if (memblock_reserve(fw_dump.param_area, COMMAND_LINE_SIZE)) { >>>>> pr_warn("WARNING: Can't use additional parameters area!\n"); >>>>> fw_dump.param_area = 0; >>>>> -- >>>>> 2.46.2
Sourabh Jain <sourabhjain@linux.ibm.com> writes: > Hello Ritesh, > > > On 12/11/24 17:23, Ritesh Harjani (IBM) wrote: >> Ritesh Harjani (IBM) <ritesh.list@gmail.com> writes: >> >>> Sourabh Jain <sourabhjain@linux.ibm.com> writes: >>> >>>> Hello Ritesh, >>>> >>>> >>>> On 12/11/24 11:51, Ritesh Harjani (IBM) wrote: >>>>> Sourabh Jain <sourabhjain@linux.ibm.com> writes: >>>>> >>>>>> The param area is a memory region where the kernel places additional >>>>>> command-line arguments for fadump kernel. Currently, the param memory >>>>>> area is reserved in fadump kernel if it is above boot_mem_top. However, >>>>>> it should be reserved if it is below boot_mem_top because the fadump >>>>>> kernel already reserves memory from boot_mem_top to the end of DRAM. >>>>> did you mean s/reserves/preserves ? >>>> Yeah, preserves is better. >>>> >>>>>> Currently, there is no impact from not reserving param memory if it is >>>>>> below boot_mem_top, as it is not used after the early boot phase of the >>>>>> fadump kernel. However, if this changes in the future, it could lead to >>>>>> issues in the fadump kernel. >>>>> This will only affect Hash and not radix correct? Because for radix your >>>>> param_area is somewhere within [memblock_end_of_DRAM() / 2, memblock_end_of_DRAM()] >>>>> which is anyway above boot_mem_top so it is anyway preserved as is... >>>> Yes. >>>> >>>>> ... On second thoughts since param_area during normal kernel boot anyway >>>>> comes from memblock now. And irrespective of where it falls (above or below >>>>> boot_mem_top), we anyway append the bootargs to that. So we don't really >>>>> preserve the original contents :) right? >>>> Sorry I didn't get it. We append strings from param_area to >>>> boot_command_line >>>> not the other way. >>>> >>>> >>> Right. My bad. >>> >>>>> So why not just always call for >>>>> memblock_reserve() on param_area during capture kernel run? >>>>> >>>>> Thoughts? >>>> Yes, there is no harm in calling memblock_reserve regardless of whether >>>> param_area >>>> is below or above boot_mem_top. However, calling it when param_area is >>>> higher than >>>> boot_mem_top is redundant, as we know fadump preserves memory from >>>> boot_mem_top >>>> to the end of DRAM during early boot. >>> So if we don't reserve the param_area then the kernel may use it for >>> some other purposes once memory is released to buddy, right. But I guess, >>> given we anyway copied the param_area in fadump_append_bootargs() during >>> early boot to cmdline (before parse_early_param()), we anyway don't need >>> it for later, right? >>> >>> In that case we don't need for Hash too (i.e when param_area falls under >>> boot_mem_top), right? Since we anyway copied the param_area before >>> parse_early_param() in fadump_append_bootargs. So what is the point in >>> calling memblock_reserve() on that? Maybe I am missing something, can >>> you please help explain. >>> >> Ok. I think I got it now. You did mention in the changelog - >> >> "Currently, there is no impact from not reserving param memory if it is >> below boot_mem_top, as it is not used after the early boot phase of the >> fadump kernel. However, if this changes in the future, it could lead to >> issues in the fadump kernel." >> >> >> So it is not an issue now, since the param area is not used after the >> contents is copied over. So I think today we anyway don't need to call >> memblock_reserve() on the param area - but if we are making it future >> proof then we might as well just call memblock_reserve() on param_area >> irrespective because otherwise once the kernel starts up it might re-use >> that area for other purposes. So isn't it better to reserve for fadump >> use of the param_area for either during early boot or during late kernel >> boot phase of the capture kernel? > > Seems like there is some confusion. Here is the full picture with the > current patch: > > First kernel boot: Reserve param_area during early boot and let it > remain reserved. > > First kernel crashed > > Fadump/second kernel boot > > fadump_reserve_mem() does memblock_reserve() from boot_mem_top to > end_of_dram(). > This covers param_area if it is above boot_mem_top. > > fadump_setup_param_area() does memblock_reserve() for param_area only if > it falls below > boot_mem_top. This ensures it is covered if param_area falls below > boot_mem_top. > > This way, we make sure that param_area is preserved during the fadump > kernel's early boot in both cases. > > Note: fadump_reserve_mem() is executed before fadump_setup_param_area(). > Ohk. I think I missd to look into the dump_active portion of the code which is where the fadump calls fadump_reserve_mem() -> fadump_reserve_crash_area(). I will be pay more attention to these details the next time :) > IIUC, you are suggesting doing memblock_reserve() for param_area in > fadump_setup_param_area() regardless > of its location. If we do this, memblock_reserve() will be called twice > for the case where it falls above > boot_mem_top. I agree there is no harm in doing so, but do we have to? > > Again, I don't have a strong opinion on this but just wanted to put > things forward to make sure we are on the > same page. Let me know your opinion. No. The current patch is doing the right thing. Thanks for taking time and answering my queries. I agree with the approach and logic taken in this patch including that of the "Fixes" tag. The patch looks good to me. Please feel free to add - Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com> -ritesh
Hello Ritesh, On 12/11/24 18:40, Ritesh Harjani (IBM) wrote: > Sourabh Jain <sourabhjain@linux.ibm.com> writes: > >> Hello Ritesh, >> >> >> On 12/11/24 17:23, Ritesh Harjani (IBM) wrote: >>> Ritesh Harjani (IBM) <ritesh.list@gmail.com> writes: >>> >>>> Sourabh Jain <sourabhjain@linux.ibm.com> writes: >>>> >>>>> Hello Ritesh, >>>>> >>>>> >>>>> On 12/11/24 11:51, Ritesh Harjani (IBM) wrote: >>>>>> Sourabh Jain <sourabhjain@linux.ibm.com> writes: >>>>>> >>>>>>> The param area is a memory region where the kernel places additional >>>>>>> command-line arguments for fadump kernel. Currently, the param memory >>>>>>> area is reserved in fadump kernel if it is above boot_mem_top. However, >>>>>>> it should be reserved if it is below boot_mem_top because the fadump >>>>>>> kernel already reserves memory from boot_mem_top to the end of DRAM. >>>>>> did you mean s/reserves/preserves ? >>>>> Yeah, preserves is better. >>>>> >>>>>>> Currently, there is no impact from not reserving param memory if it is >>>>>>> below boot_mem_top, as it is not used after the early boot phase of the >>>>>>> fadump kernel. However, if this changes in the future, it could lead to >>>>>>> issues in the fadump kernel. >>>>>> This will only affect Hash and not radix correct? Because for radix your >>>>>> param_area is somewhere within [memblock_end_of_DRAM() / 2, memblock_end_of_DRAM()] >>>>>> which is anyway above boot_mem_top so it is anyway preserved as is... >>>>> Yes. >>>>> >>>>>> ... On second thoughts since param_area during normal kernel boot anyway >>>>>> comes from memblock now. And irrespective of where it falls (above or below >>>>>> boot_mem_top), we anyway append the bootargs to that. So we don't really >>>>>> preserve the original contents :) right? >>>>> Sorry I didn't get it. We append strings from param_area to >>>>> boot_command_line >>>>> not the other way. >>>>> >>>>> >>>> Right. My bad. >>>> >>>>>> So why not just always call for >>>>>> memblock_reserve() on param_area during capture kernel run? >>>>>> >>>>>> Thoughts? >>>>> Yes, there is no harm in calling memblock_reserve regardless of whether >>>>> param_area >>>>> is below or above boot_mem_top. However, calling it when param_area is >>>>> higher than >>>>> boot_mem_top is redundant, as we know fadump preserves memory from >>>>> boot_mem_top >>>>> to the end of DRAM during early boot. >>>> So if we don't reserve the param_area then the kernel may use it for >>>> some other purposes once memory is released to buddy, right. But I guess, >>>> given we anyway copied the param_area in fadump_append_bootargs() during >>>> early boot to cmdline (before parse_early_param()), we anyway don't need >>>> it for later, right? >>>> >>>> In that case we don't need for Hash too (i.e when param_area falls under >>>> boot_mem_top), right? Since we anyway copied the param_area before >>>> parse_early_param() in fadump_append_bootargs. So what is the point in >>>> calling memblock_reserve() on that? Maybe I am missing something, can >>>> you please help explain. >>>> >>> Ok. I think I got it now. You did mention in the changelog - >>> >>> "Currently, there is no impact from not reserving param memory if it is >>> below boot_mem_top, as it is not used after the early boot phase of the >>> fadump kernel. However, if this changes in the future, it could lead to >>> issues in the fadump kernel." >>> >>> >>> So it is not an issue now, since the param area is not used after the >>> contents is copied over. So I think today we anyway don't need to call >>> memblock_reserve() on the param area - but if we are making it future >>> proof then we might as well just call memblock_reserve() on param_area >>> irrespective because otherwise once the kernel starts up it might re-use >>> that area for other purposes. So isn't it better to reserve for fadump >>> use of the param_area for either during early boot or during late kernel >>> boot phase of the capture kernel? >> Seems like there is some confusion. Here is the full picture with the >> current patch: >> >> First kernel boot: Reserve param_area during early boot and let it >> remain reserved. >> >> First kernel crashed >> >> Fadump/second kernel boot >> >> fadump_reserve_mem() does memblock_reserve() from boot_mem_top to >> end_of_dram(). >> This covers param_area if it is above boot_mem_top. >> >> fadump_setup_param_area() does memblock_reserve() for param_area only if >> it falls below >> boot_mem_top. This ensures it is covered if param_area falls below >> boot_mem_top. >> >> This way, we make sure that param_area is preserved during the fadump >> kernel's early boot in both cases. >> >> Note: fadump_reserve_mem() is executed before fadump_setup_param_area(). >> > Ohk. I think I missd to look into the dump_active portion of the code > which is where the fadump calls fadump_reserve_mem() -> fadump_reserve_crash_area(). > I will be pay more attention to these details the next time :) > >> IIUC, you are suggesting doing memblock_reserve() for param_area in >> fadump_setup_param_area() regardless >> of its location. If we do this, memblock_reserve() will be called twice >> for the case where it falls above >> boot_mem_top. I agree there is no harm in doing so, but do we have to? >> >> Again, I don't have a strong opinion on this but just wanted to put >> things forward to make sure we are on the >> same page. Let me know your opinion. > No. The current patch is doing the right thing. Thanks for taking time > and answering my queries. I agree with the approach and logic taken in > this patch including that of the "Fixes" tag. > > The patch looks good to me. Please feel free to add - > > Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com> Thank you for putting in the effort to review that patch. - Sourabh Jain
diff --git a/arch/powerpc/kernel/fadump.c b/arch/powerpc/kernel/fadump.c index 3a2863307863..3f3674060164 100644 --- a/arch/powerpc/kernel/fadump.c +++ b/arch/powerpc/kernel/fadump.c @@ -143,7 +143,7 @@ void __init fadump_append_bootargs(void) if (!fw_dump.dump_active || !fw_dump.param_area_supported || !fw_dump.param_area) return; - if (fw_dump.param_area >= fw_dump.boot_mem_top) { + if (fw_dump.param_area < fw_dump.boot_mem_top) { if (memblock_reserve(fw_dump.param_area, COMMAND_LINE_SIZE)) { pr_warn("WARNING: Can't use additional parameters area!\n"); fw_dump.param_area = 0;
The param area is a memory region where the kernel places additional command-line arguments for fadump kernel. Currently, the param memory area is reserved in fadump kernel if it is above boot_mem_top. However, it should be reserved if it is below boot_mem_top because the fadump kernel already reserves memory from boot_mem_top to the end of DRAM. Currently, there is no impact from not reserving param memory if it is below boot_mem_top, as it is not used after the early boot phase of the fadump kernel. However, if this changes in the future, it could lead to issues in the fadump kernel. Fixes: 3416c9daa6b1 ("powerpc/fadump: pass additional parameters when fadump is active") Cc: Mahesh Salgaonkar <mahesh@linux.ibm.com> Cc: Michael Ellerman <mpe@ellerman.id.au> Acked-by: Hari Bathini <hbathini@linux.ibm.com> Signed-off-by: Sourabh Jain <sourabhjain@linux.ibm.com> --- Changelog: Since v1: https://lore.kernel.org/all/20241104083528.99520-1-sourabhjain@linux.ibm.com/ - Include Fixes and Acked-by tag in the commit message - No functional changes --- arch/powerpc/kernel/fadump.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)