diff mbox series

[v3,4/6] riscv: hwprobe: export Zawrs ISA extension

Message ID 20240426100820.14762-12-ajones@ventanamicro.com
State New
Headers show
Series riscv: Apply Zawrs when available | expand

Commit Message

Andrew Jones April 26, 2024, 10:08 a.m. UTC
Export Zawrs ISA extension through hwprobe.

Signed-off-by: Andrew Jones <ajones@ventanamicro.com>
---
 Documentation/arch/riscv/hwprobe.rst  | 4 ++++
 arch/riscv/include/uapi/asm/hwprobe.h | 1 +
 arch/riscv/kernel/sys_hwprobe.c       | 1 +
 3 files changed, 6 insertions(+)

Comments

Clément Léger June 18, 2024, 1:48 p.m. UTC | #1
On 26/04/2024 12:08, Andrew Jones wrote:
> Export Zawrs ISA extension through hwprobe.
> 
> Signed-off-by: Andrew Jones <ajones@ventanamicro.com>
> ---
>  Documentation/arch/riscv/hwprobe.rst  | 4 ++++
>  arch/riscv/include/uapi/asm/hwprobe.h | 1 +
>  arch/riscv/kernel/sys_hwprobe.c       | 1 +
>  3 files changed, 6 insertions(+)
> 
> diff --git a/Documentation/arch/riscv/hwprobe.rst b/Documentation/arch/riscv/hwprobe.rst
> index b2bcc9eed9aa..e072ce8285d8 100644
> --- a/Documentation/arch/riscv/hwprobe.rst
> +++ b/Documentation/arch/riscv/hwprobe.rst
> @@ -188,6 +188,10 @@ The following keys are defined:
>         manual starting from commit 95cf1f9 ("Add changes requested by Ved
>         during signoff")
>  
> +  * :c:macro:`RISCV_HWPROBE_EXT_ZAWRS`: The Zawrs extension is supported as
> +       ratified in commit 98918c844281 ("Merge pull request #1217 from
> +       riscv/zawrs") of riscv-isa-manual.
> +
>  * :c:macro:`RISCV_HWPROBE_KEY_CPUPERF_0`: A bitmask that contains performance
>    information about the selected set of processors.
>  
> diff --git a/arch/riscv/include/uapi/asm/hwprobe.h b/arch/riscv/include/uapi/asm/hwprobe.h
> index 9f2a8e3ff204..a5fca3878a32 100644
> --- a/arch/riscv/include/uapi/asm/hwprobe.h
> +++ b/arch/riscv/include/uapi/asm/hwprobe.h
> @@ -59,6 +59,7 @@ struct riscv_hwprobe {
>  #define		RISCV_HWPROBE_EXT_ZTSO		(1ULL << 33)
>  #define		RISCV_HWPROBE_EXT_ZACAS		(1ULL << 34)
>  #define		RISCV_HWPROBE_EXT_ZICOND	(1ULL << 35)
> +#define		RISCV_HWPROBE_EXT_ZAWRS		(1ULL << 36)
>  #define RISCV_HWPROBE_KEY_CPUPERF_0	5
>  #define		RISCV_HWPROBE_MISALIGNED_UNKNOWN	(0 << 0)
>  #define		RISCV_HWPROBE_MISALIGNED_EMULATED	(1 << 0)
> diff --git a/arch/riscv/kernel/sys_hwprobe.c b/arch/riscv/kernel/sys_hwprobe.c
> index 8cae41a502dd..b86e3531a45a 100644
> --- a/arch/riscv/kernel/sys_hwprobe.c
> +++ b/arch/riscv/kernel/sys_hwprobe.c
> @@ -111,6 +111,7 @@ static void hwprobe_isa_ext0(struct riscv_hwprobe *pair,
>  		EXT_KEY(ZTSO);
>  		EXT_KEY(ZACAS);
>  		EXT_KEY(ZICOND);
> +		EXT_KEY(ZAWRS);
>  
>  		if (has_vector()) {
>  			EXT_KEY(ZVBB);

AFAIU, when used in userspace, this will actually "stall" the processor
until an interrupt/timeout happens, so the current process will keep
occupying the processor doing nothing (up to the next interrupt/timeout)
right ?

BTW, the spec also states that "When the TW (Timeout Wait) bit in
mstatus is set and WRS.NTO is executed in any privilege mode other than
M mode, and it does not complete within an implementation-specific
bounded time limit, the WRS.NTO instruction will cause an illegal
instruction exception." so I guess the process will be killed in this case ?

If this is not a concern:

Reviewed-by: Clément Léger <cleger@rivosinc.com>

Thanks,

Clément
Andrew Jones June 18, 2024, 4:01 p.m. UTC | #2
On Tue, Jun 18, 2024 at 03:48:59PM GMT, Clément Léger wrote:
> 
> 
> On 26/04/2024 12:08, Andrew Jones wrote:
> > Export Zawrs ISA extension through hwprobe.
> > 
> > Signed-off-by: Andrew Jones <ajones@ventanamicro.com>
> > ---
> >  Documentation/arch/riscv/hwprobe.rst  | 4 ++++
> >  arch/riscv/include/uapi/asm/hwprobe.h | 1 +
> >  arch/riscv/kernel/sys_hwprobe.c       | 1 +
> >  3 files changed, 6 insertions(+)
> > 
> > diff --git a/Documentation/arch/riscv/hwprobe.rst b/Documentation/arch/riscv/hwprobe.rst
> > index b2bcc9eed9aa..e072ce8285d8 100644
> > --- a/Documentation/arch/riscv/hwprobe.rst
> > +++ b/Documentation/arch/riscv/hwprobe.rst
> > @@ -188,6 +188,10 @@ The following keys are defined:
> >         manual starting from commit 95cf1f9 ("Add changes requested by Ved
> >         during signoff")
> >  
> > +  * :c:macro:`RISCV_HWPROBE_EXT_ZAWRS`: The Zawrs extension is supported as
> > +       ratified in commit 98918c844281 ("Merge pull request #1217 from
> > +       riscv/zawrs") of riscv-isa-manual.
> > +
> >  * :c:macro:`RISCV_HWPROBE_KEY_CPUPERF_0`: A bitmask that contains performance
> >    information about the selected set of processors.
> >  
> > diff --git a/arch/riscv/include/uapi/asm/hwprobe.h b/arch/riscv/include/uapi/asm/hwprobe.h
> > index 9f2a8e3ff204..a5fca3878a32 100644
> > --- a/arch/riscv/include/uapi/asm/hwprobe.h
> > +++ b/arch/riscv/include/uapi/asm/hwprobe.h
> > @@ -59,6 +59,7 @@ struct riscv_hwprobe {
> >  #define		RISCV_HWPROBE_EXT_ZTSO		(1ULL << 33)
> >  #define		RISCV_HWPROBE_EXT_ZACAS		(1ULL << 34)
> >  #define		RISCV_HWPROBE_EXT_ZICOND	(1ULL << 35)
> > +#define		RISCV_HWPROBE_EXT_ZAWRS		(1ULL << 36)
> >  #define RISCV_HWPROBE_KEY_CPUPERF_0	5
> >  #define		RISCV_HWPROBE_MISALIGNED_UNKNOWN	(0 << 0)
> >  #define		RISCV_HWPROBE_MISALIGNED_EMULATED	(1 << 0)
> > diff --git a/arch/riscv/kernel/sys_hwprobe.c b/arch/riscv/kernel/sys_hwprobe.c
> > index 8cae41a502dd..b86e3531a45a 100644
> > --- a/arch/riscv/kernel/sys_hwprobe.c
> > +++ b/arch/riscv/kernel/sys_hwprobe.c
> > @@ -111,6 +111,7 @@ static void hwprobe_isa_ext0(struct riscv_hwprobe *pair,
> >  		EXT_KEY(ZTSO);
> >  		EXT_KEY(ZACAS);
> >  		EXT_KEY(ZICOND);
> > +		EXT_KEY(ZAWRS);
> >  
> >  		if (has_vector()) {
> >  			EXT_KEY(ZVBB);
> 
> AFAIU, when used in userspace, this will actually "stall" the processor
> until an interrupt/timeout happens, so the current process will keep
> occupying the processor doing nothing (up to the next interrupt/timeout)
> right ?

Yes, but of course the OS can always preempt the task as well.

> 
> BTW, the spec also states that "When the TW (Timeout Wait) bit in
> mstatus is set and WRS.NTO is executed in any privilege mode other than
> M mode, and it does not complete within an implementation-specific
> bounded time limit, the WRS.NTO instruction will cause an illegal
> instruction exception." so I guess the process will be killed in this case ?

We don't expect mstatus.TW to be set. If it is, then wfi would likely kill
the kernel before wrs.nto gets a chance to, but one or the other will
certainly ensure usermode never gets a chance to try it :-)

We have a handful of these assumptions about how M-mode has configured
things prior to Linux starting. It'd be good if we documented them all
somewhere.

> 
> If this is not a concern:
> 
> Reviewed-by: Clément Léger <cleger@rivosinc.com>

Thanks,
drew
Conor Dooley June 18, 2024, 4:59 p.m. UTC | #3
On Tue, Jun 18, 2024 at 06:01:04PM +0200, Andrew Jones wrote:
> On Tue, Jun 18, 2024 at 03:48:59PM GMT, Clément Léger wrote:
> > 
> > 
> > On 26/04/2024 12:08, Andrew Jones wrote:
> > > Export Zawrs ISA extension through hwprobe.
> > > 
> > > Signed-off-by: Andrew Jones <ajones@ventanamicro.com>
> > > ---
> > >  Documentation/arch/riscv/hwprobe.rst  | 4 ++++
> > >  arch/riscv/include/uapi/asm/hwprobe.h | 1 +
> > >  arch/riscv/kernel/sys_hwprobe.c       | 1 +
> > >  3 files changed, 6 insertions(+)
> > > 
> > > diff --git a/Documentation/arch/riscv/hwprobe.rst b/Documentation/arch/riscv/hwprobe.rst
> > > index b2bcc9eed9aa..e072ce8285d8 100644
> > > --- a/Documentation/arch/riscv/hwprobe.rst
> > > +++ b/Documentation/arch/riscv/hwprobe.rst
> > > @@ -188,6 +188,10 @@ The following keys are defined:
> > >         manual starting from commit 95cf1f9 ("Add changes requested by Ved
> > >         during signoff")
> > >  
> > > +  * :c:macro:`RISCV_HWPROBE_EXT_ZAWRS`: The Zawrs extension is supported as
> > > +       ratified in commit 98918c844281 ("Merge pull request #1217 from
> > > +       riscv/zawrs") of riscv-isa-manual.
> > > +
> > >  * :c:macro:`RISCV_HWPROBE_KEY_CPUPERF_0`: A bitmask that contains performance
> > >    information about the selected set of processors.
> > >  
> > > diff --git a/arch/riscv/include/uapi/asm/hwprobe.h b/arch/riscv/include/uapi/asm/hwprobe.h
> > > index 9f2a8e3ff204..a5fca3878a32 100644
> > > --- a/arch/riscv/include/uapi/asm/hwprobe.h
> > > +++ b/arch/riscv/include/uapi/asm/hwprobe.h
> > > @@ -59,6 +59,7 @@ struct riscv_hwprobe {
> > >  #define		RISCV_HWPROBE_EXT_ZTSO		(1ULL << 33)
> > >  #define		RISCV_HWPROBE_EXT_ZACAS		(1ULL << 34)
> > >  #define		RISCV_HWPROBE_EXT_ZICOND	(1ULL << 35)
> > > +#define		RISCV_HWPROBE_EXT_ZAWRS		(1ULL << 36)
> > >  #define RISCV_HWPROBE_KEY_CPUPERF_0	5
> > >  #define		RISCV_HWPROBE_MISALIGNED_UNKNOWN	(0 << 0)
> > >  #define		RISCV_HWPROBE_MISALIGNED_EMULATED	(1 << 0)
> > > diff --git a/arch/riscv/kernel/sys_hwprobe.c b/arch/riscv/kernel/sys_hwprobe.c
> > > index 8cae41a502dd..b86e3531a45a 100644
> > > --- a/arch/riscv/kernel/sys_hwprobe.c
> > > +++ b/arch/riscv/kernel/sys_hwprobe.c
> > > @@ -111,6 +111,7 @@ static void hwprobe_isa_ext0(struct riscv_hwprobe *pair,
> > >  		EXT_KEY(ZTSO);
> > >  		EXT_KEY(ZACAS);
> > >  		EXT_KEY(ZICOND);
> > > +		EXT_KEY(ZAWRS);
> > >  
> > >  		if (has_vector()) {
> > >  			EXT_KEY(ZVBB);
> > 
> > AFAIU, when used in userspace, this will actually "stall" the processor
> > until an interrupt/timeout happens, so the current process will keep
> > occupying the processor doing nothing (up to the next interrupt/timeout)
> > right ?
> 
> Yes, but of course the OS can always preempt the task as well.
> 
> > 
> > BTW, the spec also states that "When the TW (Timeout Wait) bit in
> > mstatus is set and WRS.NTO is executed in any privilege mode other than
> > M mode, and it does not complete within an implementation-specific
> > bounded time limit, the WRS.NTO instruction will cause an illegal
> > instruction exception." so I guess the process will be killed in this case ?
> 
> We don't expect mstatus.TW to be set. If it is, then wfi would likely kill
> the kernel before wrs.nto gets a chance to, but one or the other will
> certainly ensure usermode never gets a chance to try it :-)
> 
> We have a handful of these assumptions about how M-mode has configured
> things prior to Linux starting. It'd be good if we documented them all
> somewhere.

Boot.rst :) If you're adding a new assumption, I think it should go
there.
Andrew Jones June 18, 2024, 5:05 p.m. UTC | #4
On Tue, Jun 18, 2024 at 05:59:22PM GMT, Conor Dooley wrote:
> On Tue, Jun 18, 2024 at 06:01:04PM +0200, Andrew Jones wrote:
> > On Tue, Jun 18, 2024 at 03:48:59PM GMT, Clément Léger wrote:
> > > 
> > > 
> > > On 26/04/2024 12:08, Andrew Jones wrote:
> > > > Export Zawrs ISA extension through hwprobe.
> > > > 
> > > > Signed-off-by: Andrew Jones <ajones@ventanamicro.com>
> > > > ---
> > > >  Documentation/arch/riscv/hwprobe.rst  | 4 ++++
> > > >  arch/riscv/include/uapi/asm/hwprobe.h | 1 +
> > > >  arch/riscv/kernel/sys_hwprobe.c       | 1 +
> > > >  3 files changed, 6 insertions(+)
> > > > 
> > > > diff --git a/Documentation/arch/riscv/hwprobe.rst b/Documentation/arch/riscv/hwprobe.rst
> > > > index b2bcc9eed9aa..e072ce8285d8 100644
> > > > --- a/Documentation/arch/riscv/hwprobe.rst
> > > > +++ b/Documentation/arch/riscv/hwprobe.rst
> > > > @@ -188,6 +188,10 @@ The following keys are defined:
> > > >         manual starting from commit 95cf1f9 ("Add changes requested by Ved
> > > >         during signoff")
> > > >  
> > > > +  * :c:macro:`RISCV_HWPROBE_EXT_ZAWRS`: The Zawrs extension is supported as
> > > > +       ratified in commit 98918c844281 ("Merge pull request #1217 from
> > > > +       riscv/zawrs") of riscv-isa-manual.
> > > > +
> > > >  * :c:macro:`RISCV_HWPROBE_KEY_CPUPERF_0`: A bitmask that contains performance
> > > >    information about the selected set of processors.
> > > >  
> > > > diff --git a/arch/riscv/include/uapi/asm/hwprobe.h b/arch/riscv/include/uapi/asm/hwprobe.h
> > > > index 9f2a8e3ff204..a5fca3878a32 100644
> > > > --- a/arch/riscv/include/uapi/asm/hwprobe.h
> > > > +++ b/arch/riscv/include/uapi/asm/hwprobe.h
> > > > @@ -59,6 +59,7 @@ struct riscv_hwprobe {
> > > >  #define		RISCV_HWPROBE_EXT_ZTSO		(1ULL << 33)
> > > >  #define		RISCV_HWPROBE_EXT_ZACAS		(1ULL << 34)
> > > >  #define		RISCV_HWPROBE_EXT_ZICOND	(1ULL << 35)
> > > > +#define		RISCV_HWPROBE_EXT_ZAWRS		(1ULL << 36)
> > > >  #define RISCV_HWPROBE_KEY_CPUPERF_0	5
> > > >  #define		RISCV_HWPROBE_MISALIGNED_UNKNOWN	(0 << 0)
> > > >  #define		RISCV_HWPROBE_MISALIGNED_EMULATED	(1 << 0)
> > > > diff --git a/arch/riscv/kernel/sys_hwprobe.c b/arch/riscv/kernel/sys_hwprobe.c
> > > > index 8cae41a502dd..b86e3531a45a 100644
> > > > --- a/arch/riscv/kernel/sys_hwprobe.c
> > > > +++ b/arch/riscv/kernel/sys_hwprobe.c
> > > > @@ -111,6 +111,7 @@ static void hwprobe_isa_ext0(struct riscv_hwprobe *pair,
> > > >  		EXT_KEY(ZTSO);
> > > >  		EXT_KEY(ZACAS);
> > > >  		EXT_KEY(ZICOND);
> > > > +		EXT_KEY(ZAWRS);
> > > >  
> > > >  		if (has_vector()) {
> > > >  			EXT_KEY(ZVBB);
> > > 
> > > AFAIU, when used in userspace, this will actually "stall" the processor
> > > until an interrupt/timeout happens, so the current process will keep
> > > occupying the processor doing nothing (up to the next interrupt/timeout)
> > > right ?
> > 
> > Yes, but of course the OS can always preempt the task as well.
> > 
> > > 
> > > BTW, the spec also states that "When the TW (Timeout Wait) bit in
> > > mstatus is set and WRS.NTO is executed in any privilege mode other than
> > > M mode, and it does not complete within an implementation-specific
> > > bounded time limit, the WRS.NTO instruction will cause an illegal
> > > instruction exception." so I guess the process will be killed in this case ?
> > 
> > We don't expect mstatus.TW to be set. If it is, then wfi would likely kill
> > the kernel before wrs.nto gets a chance to, but one or the other will
> > certainly ensure usermode never gets a chance to try it :-)
> > 
> > We have a handful of these assumptions about how M-mode has configured
> > things prior to Linux starting. It'd be good if we documented them all
> > somewhere.
> 
> Boot.rst :) If you're adding a new assumption, I think it should go
> there.

It's an old assumption (wfi has been counting on it since the beginning of
time). But documenting it, along with anything else similar to it, in
boot.rst is a good idea. I've added that to my TODO.

Thanks,
drew
Conor Dooley June 18, 2024, 5:34 p.m. UTC | #5
On Tue, Jun 18, 2024 at 07:05:41PM +0200, Andrew Jones wrote:
> On Tue, Jun 18, 2024 at 05:59:22PM GMT, Conor Dooley wrote:
> > On Tue, Jun 18, 2024 at 06:01:04PM +0200, Andrew Jones wrote:
> > > On Tue, Jun 18, 2024 at 03:48:59PM GMT, Clément Léger wrote:
> > > > On 26/04/2024 12:08, Andrew Jones wrote:

> > > > 
> > > > BTW, the spec also states that "When the TW (Timeout Wait) bit in
> > > > mstatus is set and WRS.NTO is executed in any privilege mode other than
> > > > M mode, and it does not complete within an implementation-specific
> > > > bounded time limit, the WRS.NTO instruction will cause an illegal
> > > > instruction exception." so I guess the process will be killed in this case ?
> > > 
> > > We don't expect mstatus.TW to be set. If it is, then wfi would likely kill
> > > the kernel before wrs.nto gets a chance to, but one or the other will
> > > certainly ensure usermode never gets a chance to try it :-)
> > > 
> > > We have a handful of these assumptions about how M-mode has configured
> > > things prior to Linux starting. It'd be good if we documented them all
> > > somewhere.
> > 
> > Boot.rst :) If you're adding a new assumption, I think it should go
> > there.
> 
> It's an old assumption (wfi has been counting on it since the beginning of
> time). But documenting it, along with anything else similar to it, in
> boot.rst is a good idea. I've added that to my TODO.

Misunderstanding of "new" I think, I meant new to documentation not just
new to the kernel :)
diff mbox series

Patch

diff --git a/Documentation/arch/riscv/hwprobe.rst b/Documentation/arch/riscv/hwprobe.rst
index b2bcc9eed9aa..e072ce8285d8 100644
--- a/Documentation/arch/riscv/hwprobe.rst
+++ b/Documentation/arch/riscv/hwprobe.rst
@@ -188,6 +188,10 @@  The following keys are defined:
        manual starting from commit 95cf1f9 ("Add changes requested by Ved
        during signoff")
 
+  * :c:macro:`RISCV_HWPROBE_EXT_ZAWRS`: The Zawrs extension is supported as
+       ratified in commit 98918c844281 ("Merge pull request #1217 from
+       riscv/zawrs") of riscv-isa-manual.
+
 * :c:macro:`RISCV_HWPROBE_KEY_CPUPERF_0`: A bitmask that contains performance
   information about the selected set of processors.
 
diff --git a/arch/riscv/include/uapi/asm/hwprobe.h b/arch/riscv/include/uapi/asm/hwprobe.h
index 9f2a8e3ff204..a5fca3878a32 100644
--- a/arch/riscv/include/uapi/asm/hwprobe.h
+++ b/arch/riscv/include/uapi/asm/hwprobe.h
@@ -59,6 +59,7 @@  struct riscv_hwprobe {
 #define		RISCV_HWPROBE_EXT_ZTSO		(1ULL << 33)
 #define		RISCV_HWPROBE_EXT_ZACAS		(1ULL << 34)
 #define		RISCV_HWPROBE_EXT_ZICOND	(1ULL << 35)
+#define		RISCV_HWPROBE_EXT_ZAWRS		(1ULL << 36)
 #define RISCV_HWPROBE_KEY_CPUPERF_0	5
 #define		RISCV_HWPROBE_MISALIGNED_UNKNOWN	(0 << 0)
 #define		RISCV_HWPROBE_MISALIGNED_EMULATED	(1 << 0)
diff --git a/arch/riscv/kernel/sys_hwprobe.c b/arch/riscv/kernel/sys_hwprobe.c
index 8cae41a502dd..b86e3531a45a 100644
--- a/arch/riscv/kernel/sys_hwprobe.c
+++ b/arch/riscv/kernel/sys_hwprobe.c
@@ -111,6 +111,7 @@  static void hwprobe_isa_ext0(struct riscv_hwprobe *pair,
 		EXT_KEY(ZTSO);
 		EXT_KEY(ZACAS);
 		EXT_KEY(ZICOND);
+		EXT_KEY(ZAWRS);
 
 		if (has_vector()) {
 			EXT_KEY(ZVBB);