| Message ID | 20240805050829.297171-1-sourabhjain@linux.ibm.com (mailing list archive) |
|---|---|
| State | Handled Elsewhere |
| Headers | show |
| Series | Document/kexec: Generalize crash hotplug description | expand |
| Context | Check | Description |
|---|---|---|
| snowpatch_ozlabs/github-powerpc_sparse | success | Successfully ran 4 jobs. |
| snowpatch_ozlabs/github-powerpc_clang | success | Successfully ran 5 jobs. |
| snowpatch_ozlabs/github-powerpc_kernel_qemu | success | Successfully ran 21 jobs. |
Hi Sourabh, sorry for late reply, was on vacation and then catching up... On Mon, 5 Aug 2024 10:38:29 +0530 Sourabh Jain <sourabhjain@linux.ibm.com> wrote: > Commit 79365026f869 ("crash: add a new kexec flag for hotplug support") > generalizes the crash hotplug support to allow architectures to update > multiple kexec segments on CPU/Memory hotplug and not just elfcorehdr. > Therefore, update the relevant kernel documentation to reflect the same. > > No functional change. > > Cc: Petr Tesarik <petr@tesarici.cz> > Cc: Hari Bathini <hbathini@linux.ibm.com> > Cc: kexec@lists.infradead.org > Cc: linux-kernel@vger.kernel.org > Cc: linuxppc-dev@lists.ozlabs.org > Cc: x86@kernel.org > Signed-off-by: Sourabh Jain <sourabhjain@linux.ibm.com> > --- > > Discussion about the documentation update: > https://lore.kernel.org/all/68d0328d-531a-4a2b-ab26-c97fd8a12e8b@linux.ibm.com/ > > --- > .../ABI/testing/sysfs-devices-memory | 6 ++-- > .../ABI/testing/sysfs-devices-system-cpu | 6 ++-- > .../admin-guide/mm/memory-hotplug.rst | 5 ++-- > Documentation/core-api/cpu_hotplug.rst | 10 ++++--- > kernel/crash_core.c | 29 ++++++++++++------- > 5 files changed, 33 insertions(+), 23 deletions(-) > > diff --git a/Documentation/ABI/testing/sysfs-devices-memory b/Documentation/ABI/testing/sysfs-devices-memory > index a95e0f17c35a..421acc8e2c6b 100644 > --- a/Documentation/ABI/testing/sysfs-devices-memory > +++ b/Documentation/ABI/testing/sysfs-devices-memory > @@ -115,6 +115,6 @@ What: /sys/devices/system/memory/crash_hotplug > Date: Aug 2023 > Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> > Description: > - (RO) indicates whether or not the kernel directly supports > - modifying the crash elfcorehdr for memory hot un/plug and/or > - on/offline changes. > + (RO) indicates whether or not the kernel update of kexec > + segments on memory hot un/plug and/or on/offline events, > + avoiding the need to reload kdump kernel. This sentence somehow lacks a verb. My suggestion: (RO) indicates whether or not the kernel updates relevant kexec segments on memory hot un/plug and/or on/offline events, avoiding the need to reload kdump kernel. > diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu > index 325873385b71..f4ada1cd2f96 100644 > --- a/Documentation/ABI/testing/sysfs-devices-system-cpu > +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu > @@ -703,9 +703,9 @@ What: /sys/devices/system/cpu/crash_hotplug > Date: Aug 2023 > Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> > Description: > - (RO) indicates whether or not the kernel directly supports > - modifying the crash elfcorehdr for CPU hot un/plug and/or > - on/offline changes. > + (RO) indicates whether or not the kernel update of kexec > + segments on CPU hot un/plug and/or on/offline events, > + avoiding the need to reload kdump kernel. Same as above. Otherwise LGTM. Petr T
On 08/05/24 at 10:38am, Sourabh Jain wrote: > Commit 79365026f869 ("crash: add a new kexec flag for hotplug support") > generalizes the crash hotplug support to allow architectures to update > multiple kexec segments on CPU/Memory hotplug and not just elfcorehdr. > Therefore, update the relevant kernel documentation to reflect the same. > > No functional change. > > Cc: Petr Tesarik <petr@tesarici.cz> > Cc: Hari Bathini <hbathini@linux.ibm.com> > Cc: kexec@lists.infradead.org > Cc: linux-kernel@vger.kernel.org > Cc: linuxppc-dev@lists.ozlabs.org > Cc: x86@kernel.org > Signed-off-by: Sourabh Jain <sourabhjain@linux.ibm.com> > --- > > Discussion about the documentation update: > https://lore.kernel.org/all/68d0328d-531a-4a2b-ab26-c97fd8a12e8b@linux.ibm.com/ > > --- > .../ABI/testing/sysfs-devices-memory | 6 ++-- > .../ABI/testing/sysfs-devices-system-cpu | 6 ++-- > .../admin-guide/mm/memory-hotplug.rst | 5 ++-- > Documentation/core-api/cpu_hotplug.rst | 10 ++++--- > kernel/crash_core.c | 29 ++++++++++++------- > 5 files changed, 33 insertions(+), 23 deletions(-) The overall looks good to me, except of concern from Petr. Thanks. > > diff --git a/Documentation/ABI/testing/sysfs-devices-memory b/Documentation/ABI/testing/sysfs-devices-memory > index a95e0f17c35a..421acc8e2c6b 100644 > --- a/Documentation/ABI/testing/sysfs-devices-memory > +++ b/Documentation/ABI/testing/sysfs-devices-memory > @@ -115,6 +115,6 @@ What: /sys/devices/system/memory/crash_hotplug > Date: Aug 2023 > Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> > Description: > - (RO) indicates whether or not the kernel directly supports > - modifying the crash elfcorehdr for memory hot un/plug and/or > - on/offline changes. > + (RO) indicates whether or not the kernel update of kexec > + segments on memory hot un/plug and/or on/offline events, > + avoiding the need to reload kdump kernel. > diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu > index 325873385b71..f4ada1cd2f96 100644 > --- a/Documentation/ABI/testing/sysfs-devices-system-cpu > +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu > @@ -703,9 +703,9 @@ What: /sys/devices/system/cpu/crash_hotplug > Date: Aug 2023 > Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> > Description: > - (RO) indicates whether or not the kernel directly supports > - modifying the crash elfcorehdr for CPU hot un/plug and/or > - on/offline changes. > + (RO) indicates whether or not the kernel update of kexec > + segments on CPU hot un/plug and/or on/offline events, > + avoiding the need to reload kdump kernel. > > What: /sys/devices/system/cpu/enabled > Date: Nov 2022 > diff --git a/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst > index 098f14d83e99..cb2c080f400c 100644 > --- a/Documentation/admin-guide/mm/memory-hotplug.rst > +++ b/Documentation/admin-guide/mm/memory-hotplug.rst > @@ -294,8 +294,9 @@ The following files are currently defined: > ``crash_hotplug`` read-only: when changes to the system memory map > occur due to hot un/plug of memory, this file contains > '1' if the kernel updates the kdump capture kernel memory > - map itself (via elfcorehdr), or '0' if userspace must update > - the kdump capture kernel memory map. > + map itself (via elfcorehdr and other relevant kexec > + segments), or '0' if userspace must update the kdump > + capture kernel memory map. > > Availability depends on the CONFIG_MEMORY_HOTPLUG kernel > configuration option. > diff --git a/Documentation/core-api/cpu_hotplug.rst b/Documentation/core-api/cpu_hotplug.rst > index dcb0e379e5e8..a21dbf261be7 100644 > --- a/Documentation/core-api/cpu_hotplug.rst > +++ b/Documentation/core-api/cpu_hotplug.rst > @@ -737,8 +737,9 @@ can process the event further. > > When changes to the CPUs in the system occur, the sysfs file > /sys/devices/system/cpu/crash_hotplug contains '1' if the kernel > -updates the kdump capture kernel list of CPUs itself (via elfcorehdr), > -or '0' if userspace must update the kdump capture kernel list of CPUs. > +updates the kdump capture kernel list of CPUs itself (via elfcorehdr and > +other relevant kexec segment), or '0' if userspace must update the kdump > +capture kernel list of CPUs. > > The availability depends on the CONFIG_HOTPLUG_CPU kernel configuration > option. > @@ -750,8 +751,9 @@ file can be used in a udev rule as follows: > SUBSYSTEM=="cpu", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end" > > For a CPU hot un/plug event, if the architecture supports kernel updates > -of the elfcorehdr (which contains the list of CPUs), then the rule skips > -the unload-then-reload of the kdump capture kernel. > +of the elfcorehdr (which contains the list of CPUs) and other relevant > +kexec segments, then the rule skips the unload-then-reload of the kdump > +capture kernel. > > Kernel Inline Documentations Reference > ====================================== > diff --git a/kernel/crash_core.c b/kernel/crash_core.c > index 63cf89393c6e..64dad01e260b 100644 > --- a/kernel/crash_core.c > +++ b/kernel/crash_core.c > @@ -520,18 +520,25 @@ int crash_check_hotplug_support(void) > } > > /* > - * To accurately reflect hot un/plug changes of cpu and memory resources > - * (including onling and offlining of those resources), the elfcorehdr > - * (which is passed to the crash kernel via the elfcorehdr= parameter) > - * must be updated with the new list of CPUs and memories. > + * To accurately reflect hot un/plug changes of CPU and Memory resources > + * (including onling and offlining of those resources), the relevant > + * kexec segments must be updated with latest CPU and Memory resources. > * > - * In order to make changes to elfcorehdr, two conditions are needed: > - * First, the segment containing the elfcorehdr must be large enough > - * to permit a growing number of resources; the elfcorehdr memory size > - * is based on NR_CPUS_DEFAULT and CRASH_MAX_MEMORY_RANGES. > - * Second, purgatory must explicitly exclude the elfcorehdr from the > - * list of segments it checks (since the elfcorehdr changes and thus > - * would require an update to purgatory itself to update the digest). > + * Architectures must ensure two things for all segments that need > + * updating during hotplug events: > + * > + * 1. Segments must be large enough to accommodate a growing number of > + * resources. > + * 2. Exclude the segments from SHA verification. > + * > + * For example, on most architectures, the elfcorehdr (which is passed > + * to the crash kernel via the elfcorehdr= parameter) must include the > + * new list of CPUs and memory. To make changes to the elfcorehdr, it > + * should be large enough to permit a growing number of CPU and Memory > + * resources. One can estimate the elfcorehdr memory size based on > + * NR_CPUS_DEFAULT and CRASH_MAX_MEMORY_RANGES. The elfcorehdr is > + * excluded from SHA verification by default if the architecture > + * supports crash hotplug. > */ > static void crash_handle_hotplug_event(unsigned int hp_action, unsigned int cpu, void *arg) > { > -- > 2.45.2 >
Hello Petr, On 08/08/24 16:54, Petr Tesařík wrote: > Hi Sourabh, > > sorry for late reply, was on vacation and then catching up... > > On Mon, 5 Aug 2024 10:38:29 +0530 > Sourabh Jain <sourabhjain@linux.ibm.com> wrote: > >> Commit 79365026f869 ("crash: add a new kexec flag for hotplug support") >> generalizes the crash hotplug support to allow architectures to update >> multiple kexec segments on CPU/Memory hotplug and not just elfcorehdr. >> Therefore, update the relevant kernel documentation to reflect the same. >> >> No functional change. >> >> Cc: Petr Tesarik <petr@tesarici.cz> >> Cc: Hari Bathini <hbathini@linux.ibm.com> >> Cc: kexec@lists.infradead.org >> Cc: linux-kernel@vger.kernel.org >> Cc: linuxppc-dev@lists.ozlabs.org >> Cc: x86@kernel.org >> Signed-off-by: Sourabh Jain <sourabhjain@linux.ibm.com> >> --- >> >> Discussion about the documentation update: >> https://lore.kernel.org/all/68d0328d-531a-4a2b-ab26-c97fd8a12e8b@linux.ibm.com/ >> >> --- >> .../ABI/testing/sysfs-devices-memory | 6 ++-- >> .../ABI/testing/sysfs-devices-system-cpu | 6 ++-- >> .../admin-guide/mm/memory-hotplug.rst | 5 ++-- >> Documentation/core-api/cpu_hotplug.rst | 10 ++++--- >> kernel/crash_core.c | 29 ++++++++++++------- >> 5 files changed, 33 insertions(+), 23 deletions(-) >> >> diff --git a/Documentation/ABI/testing/sysfs-devices-memory b/Documentation/ABI/testing/sysfs-devices-memory >> index a95e0f17c35a..421acc8e2c6b 100644 >> --- a/Documentation/ABI/testing/sysfs-devices-memory >> +++ b/Documentation/ABI/testing/sysfs-devices-memory >> @@ -115,6 +115,6 @@ What: /sys/devices/system/memory/crash_hotplug >> Date: Aug 2023 >> Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> >> Description: >> - (RO) indicates whether or not the kernel directly supports >> - modifying the crash elfcorehdr for memory hot un/plug and/or >> - on/offline changes. >> + (RO) indicates whether or not the kernel update of kexec >> + segments on memory hot un/plug and/or on/offline events, >> + avoiding the need to reload kdump kernel. > This sentence somehow lacks a verb. My suggestion: > > (RO) indicates whether or not the kernel updates relevant kexec > segments on memory hot un/plug and/or on/offline events, avoiding the > need to reload kdump kernel. Thanks for the review. I will update the document as suggested. - Sourabh Jain > >> diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu >> index 325873385b71..f4ada1cd2f96 100644 >> --- a/Documentation/ABI/testing/sysfs-devices-system-cpu >> +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu >> @@ -703,9 +703,9 @@ What: /sys/devices/system/cpu/crash_hotplug >> Date: Aug 2023 >> Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> >> Description: >> - (RO) indicates whether or not the kernel directly supports >> - modifying the crash elfcorehdr for CPU hot un/plug and/or >> - on/offline changes. >> + (RO) indicates whether or not the kernel update of kexec >> + segments on CPU hot un/plug and/or on/offline events, >> + avoiding the need to reload kdump kernel. > Same as above. > > Otherwise LGTM. > > Petr T
Hello Baoquan, On 09/08/24 07:18, Baoquan He wrote: > On 08/05/24 at 10:38am, Sourabh Jain wrote: >> Commit 79365026f869 ("crash: add a new kexec flag for hotplug support") >> generalizes the crash hotplug support to allow architectures to update >> multiple kexec segments on CPU/Memory hotplug and not just elfcorehdr. >> Therefore, update the relevant kernel documentation to reflect the same. >> >> No functional change. >> >> Cc: Petr Tesarik <petr@tesarici.cz> >> Cc: Hari Bathini <hbathini@linux.ibm.com> >> Cc: kexec@lists.infradead.org >> Cc: linux-kernel@vger.kernel.org >> Cc: linuxppc-dev@lists.ozlabs.org >> Cc: x86@kernel.org >> Signed-off-by: Sourabh Jain <sourabhjain@linux.ibm.com> >> --- >> >> Discussion about the documentation update: >> https://lore.kernel.org/all/68d0328d-531a-4a2b-ab26-c97fd8a12e8b@linux.ibm.com/ >> >> --- >> .../ABI/testing/sysfs-devices-memory | 6 ++-- >> .../ABI/testing/sysfs-devices-system-cpu | 6 ++-- >> .../admin-guide/mm/memory-hotplug.rst | 5 ++-- >> Documentation/core-api/cpu_hotplug.rst | 10 ++++--- >> kernel/crash_core.c | 29 ++++++++++++------- >> 5 files changed, 33 insertions(+), 23 deletions(-) > The overall looks good to me, except of concern from Petr. Thanks. Thanks for the review. I will make the suggested changes in v2. Additionally I will also generalize the error message "kexec_trylock() failed, elfcorehdr may be inaccurate " from functions crash_handle_hotplug_event() and crash_check_hotplug_support() to "kexec_trylock() failed, kdump image may be inaccurate" - Sourabh Jain > >> diff --git a/Documentation/ABI/testing/sysfs-devices-memory b/Documentation/ABI/testing/sysfs-devices-memory >> index a95e0f17c35a..421acc8e2c6b 100644 >> --- a/Documentation/ABI/testing/sysfs-devices-memory >> +++ b/Documentation/ABI/testing/sysfs-devices-memory >> @@ -115,6 +115,6 @@ What: /sys/devices/system/memory/crash_hotplug >> Date: Aug 2023 >> Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> >> Description: >> - (RO) indicates whether or not the kernel directly supports >> - modifying the crash elfcorehdr for memory hot un/plug and/or >> - on/offline changes. >> + (RO) indicates whether or not the kernel update of kexec >> + segments on memory hot un/plug and/or on/offline events, >> + avoiding the need to reload kdump kernel. >> diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu >> index 325873385b71..f4ada1cd2f96 100644 >> --- a/Documentation/ABI/testing/sysfs-devices-system-cpu >> +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu >> @@ -703,9 +703,9 @@ What: /sys/devices/system/cpu/crash_hotplug >> Date: Aug 2023 >> Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> >> Description: >> - (RO) indicates whether or not the kernel directly supports >> - modifying the crash elfcorehdr for CPU hot un/plug and/or >> - on/offline changes. >> + (RO) indicates whether or not the kernel update of kexec >> + segments on CPU hot un/plug and/or on/offline events, >> + avoiding the need to reload kdump kernel. >> >> What: /sys/devices/system/cpu/enabled >> Date: Nov 2022 >> diff --git a/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst >> index 098f14d83e99..cb2c080f400c 100644 >> --- a/Documentation/admin-guide/mm/memory-hotplug.rst >> +++ b/Documentation/admin-guide/mm/memory-hotplug.rst >> @@ -294,8 +294,9 @@ The following files are currently defined: >> ``crash_hotplug`` read-only: when changes to the system memory map >> occur due to hot un/plug of memory, this file contains >> '1' if the kernel updates the kdump capture kernel memory >> - map itself (via elfcorehdr), or '0' if userspace must update >> - the kdump capture kernel memory map. >> + map itself (via elfcorehdr and other relevant kexec >> + segments), or '0' if userspace must update the kdump >> + capture kernel memory map. >> >> Availability depends on the CONFIG_MEMORY_HOTPLUG kernel >> configuration option. >> diff --git a/Documentation/core-api/cpu_hotplug.rst b/Documentation/core-api/cpu_hotplug.rst >> index dcb0e379e5e8..a21dbf261be7 100644 >> --- a/Documentation/core-api/cpu_hotplug.rst >> +++ b/Documentation/core-api/cpu_hotplug.rst >> @@ -737,8 +737,9 @@ can process the event further. >> >> When changes to the CPUs in the system occur, the sysfs file >> /sys/devices/system/cpu/crash_hotplug contains '1' if the kernel >> -updates the kdump capture kernel list of CPUs itself (via elfcorehdr), >> -or '0' if userspace must update the kdump capture kernel list of CPUs. >> +updates the kdump capture kernel list of CPUs itself (via elfcorehdr and >> +other relevant kexec segment), or '0' if userspace must update the kdump >> +capture kernel list of CPUs. >> >> The availability depends on the CONFIG_HOTPLUG_CPU kernel configuration >> option. >> @@ -750,8 +751,9 @@ file can be used in a udev rule as follows: >> SUBSYSTEM=="cpu", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end" >> >> For a CPU hot un/plug event, if the architecture supports kernel updates >> -of the elfcorehdr (which contains the list of CPUs), then the rule skips >> -the unload-then-reload of the kdump capture kernel. >> +of the elfcorehdr (which contains the list of CPUs) and other relevant >> +kexec segments, then the rule skips the unload-then-reload of the kdump >> +capture kernel. >> >> Kernel Inline Documentations Reference >> ====================================== >> diff --git a/kernel/crash_core.c b/kernel/crash_core.c >> index 63cf89393c6e..64dad01e260b 100644 >> --- a/kernel/crash_core.c >> +++ b/kernel/crash_core.c >> @@ -520,18 +520,25 @@ int crash_check_hotplug_support(void) >> } >> >> /* >> - * To accurately reflect hot un/plug changes of cpu and memory resources >> - * (including onling and offlining of those resources), the elfcorehdr >> - * (which is passed to the crash kernel via the elfcorehdr= parameter) >> - * must be updated with the new list of CPUs and memories. >> + * To accurately reflect hot un/plug changes of CPU and Memory resources >> + * (including onling and offlining of those resources), the relevant >> + * kexec segments must be updated with latest CPU and Memory resources. >> * >> - * In order to make changes to elfcorehdr, two conditions are needed: >> - * First, the segment containing the elfcorehdr must be large enough >> - * to permit a growing number of resources; the elfcorehdr memory size >> - * is based on NR_CPUS_DEFAULT and CRASH_MAX_MEMORY_RANGES. >> - * Second, purgatory must explicitly exclude the elfcorehdr from the >> - * list of segments it checks (since the elfcorehdr changes and thus >> - * would require an update to purgatory itself to update the digest). >> + * Architectures must ensure two things for all segments that need >> + * updating during hotplug events: >> + * >> + * 1. Segments must be large enough to accommodate a growing number of >> + * resources. >> + * 2. Exclude the segments from SHA verification. >> + * >> + * For example, on most architectures, the elfcorehdr (which is passed >> + * to the crash kernel via the elfcorehdr= parameter) must include the >> + * new list of CPUs and memory. To make changes to the elfcorehdr, it >> + * should be large enough to permit a growing number of CPU and Memory >> + * resources. One can estimate the elfcorehdr memory size based on >> + * NR_CPUS_DEFAULT and CRASH_MAX_MEMORY_RANGES. The elfcorehdr is >> + * excluded from SHA verification by default if the architecture >> + * supports crash hotplug. >> */ >> static void crash_handle_hotplug_event(unsigned int hp_action, unsigned int cpu, void *arg) >> { >> -- >> 2.45.2 >>
diff --git a/Documentation/ABI/testing/sysfs-devices-memory b/Documentation/ABI/testing/sysfs-devices-memory index a95e0f17c35a..421acc8e2c6b 100644 --- a/Documentation/ABI/testing/sysfs-devices-memory +++ b/Documentation/ABI/testing/sysfs-devices-memory @@ -115,6 +115,6 @@ What: /sys/devices/system/memory/crash_hotplug Date: Aug 2023 Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> Description: - (RO) indicates whether or not the kernel directly supports - modifying the crash elfcorehdr for memory hot un/plug and/or - on/offline changes. + (RO) indicates whether or not the kernel update of kexec + segments on memory hot un/plug and/or on/offline events, + avoiding the need to reload kdump kernel. diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu index 325873385b71..f4ada1cd2f96 100644 --- a/Documentation/ABI/testing/sysfs-devices-system-cpu +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu @@ -703,9 +703,9 @@ What: /sys/devices/system/cpu/crash_hotplug Date: Aug 2023 Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> Description: - (RO) indicates whether or not the kernel directly supports - modifying the crash elfcorehdr for CPU hot un/plug and/or - on/offline changes. + (RO) indicates whether or not the kernel update of kexec + segments on CPU hot un/plug and/or on/offline events, + avoiding the need to reload kdump kernel. What: /sys/devices/system/cpu/enabled Date: Nov 2022 diff --git a/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst index 098f14d83e99..cb2c080f400c 100644 --- a/Documentation/admin-guide/mm/memory-hotplug.rst +++ b/Documentation/admin-guide/mm/memory-hotplug.rst @@ -294,8 +294,9 @@ The following files are currently defined: ``crash_hotplug`` read-only: when changes to the system memory map occur due to hot un/plug of memory, this file contains '1' if the kernel updates the kdump capture kernel memory - map itself (via elfcorehdr), or '0' if userspace must update - the kdump capture kernel memory map. + map itself (via elfcorehdr and other relevant kexec + segments), or '0' if userspace must update the kdump + capture kernel memory map. Availability depends on the CONFIG_MEMORY_HOTPLUG kernel configuration option. diff --git a/Documentation/core-api/cpu_hotplug.rst b/Documentation/core-api/cpu_hotplug.rst index dcb0e379e5e8..a21dbf261be7 100644 --- a/Documentation/core-api/cpu_hotplug.rst +++ b/Documentation/core-api/cpu_hotplug.rst @@ -737,8 +737,9 @@ can process the event further. When changes to the CPUs in the system occur, the sysfs file /sys/devices/system/cpu/crash_hotplug contains '1' if the kernel -updates the kdump capture kernel list of CPUs itself (via elfcorehdr), -or '0' if userspace must update the kdump capture kernel list of CPUs. +updates the kdump capture kernel list of CPUs itself (via elfcorehdr and +other relevant kexec segment), or '0' if userspace must update the kdump +capture kernel list of CPUs. The availability depends on the CONFIG_HOTPLUG_CPU kernel configuration option. @@ -750,8 +751,9 @@ file can be used in a udev rule as follows: SUBSYSTEM=="cpu", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end" For a CPU hot un/plug event, if the architecture supports kernel updates -of the elfcorehdr (which contains the list of CPUs), then the rule skips -the unload-then-reload of the kdump capture kernel. +of the elfcorehdr (which contains the list of CPUs) and other relevant +kexec segments, then the rule skips the unload-then-reload of the kdump +capture kernel. Kernel Inline Documentations Reference ====================================== diff --git a/kernel/crash_core.c b/kernel/crash_core.c index 63cf89393c6e..64dad01e260b 100644 --- a/kernel/crash_core.c +++ b/kernel/crash_core.c @@ -520,18 +520,25 @@ int crash_check_hotplug_support(void) } /* - * To accurately reflect hot un/plug changes of cpu and memory resources - * (including onling and offlining of those resources), the elfcorehdr - * (which is passed to the crash kernel via the elfcorehdr= parameter) - * must be updated with the new list of CPUs and memories. + * To accurately reflect hot un/plug changes of CPU and Memory resources + * (including onling and offlining of those resources), the relevant + * kexec segments must be updated with latest CPU and Memory resources. * - * In order to make changes to elfcorehdr, two conditions are needed: - * First, the segment containing the elfcorehdr must be large enough - * to permit a growing number of resources; the elfcorehdr memory size - * is based on NR_CPUS_DEFAULT and CRASH_MAX_MEMORY_RANGES. - * Second, purgatory must explicitly exclude the elfcorehdr from the - * list of segments it checks (since the elfcorehdr changes and thus - * would require an update to purgatory itself to update the digest). + * Architectures must ensure two things for all segments that need + * updating during hotplug events: + * + * 1. Segments must be large enough to accommodate a growing number of + * resources. + * 2. Exclude the segments from SHA verification. + * + * For example, on most architectures, the elfcorehdr (which is passed + * to the crash kernel via the elfcorehdr= parameter) must include the + * new list of CPUs and memory. To make changes to the elfcorehdr, it + * should be large enough to permit a growing number of CPU and Memory + * resources. One can estimate the elfcorehdr memory size based on + * NR_CPUS_DEFAULT and CRASH_MAX_MEMORY_RANGES. The elfcorehdr is + * excluded from SHA verification by default if the architecture + * supports crash hotplug. */ static void crash_handle_hotplug_event(unsigned int hp_action, unsigned int cpu, void *arg) {
Commit 79365026f869 ("crash: add a new kexec flag for hotplug support") generalizes the crash hotplug support to allow architectures to update multiple kexec segments on CPU/Memory hotplug and not just elfcorehdr. Therefore, update the relevant kernel documentation to reflect the same. No functional change. Cc: Petr Tesarik <petr@tesarici.cz> Cc: Hari Bathini <hbathini@linux.ibm.com> Cc: kexec@lists.infradead.org Cc: linux-kernel@vger.kernel.org Cc: linuxppc-dev@lists.ozlabs.org Cc: x86@kernel.org Signed-off-by: Sourabh Jain <sourabhjain@linux.ibm.com> --- Discussion about the documentation update: https://lore.kernel.org/all/68d0328d-531a-4a2b-ab26-c97fd8a12e8b@linux.ibm.com/ --- .../ABI/testing/sysfs-devices-memory | 6 ++-- .../ABI/testing/sysfs-devices-system-cpu | 6 ++-- .../admin-guide/mm/memory-hotplug.rst | 5 ++-- Documentation/core-api/cpu_hotplug.rst | 10 ++++--- kernel/crash_core.c | 29 ++++++++++++------- 5 files changed, 33 insertions(+), 23 deletions(-)