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[PATCH v3 5/5] arm64: make the per-task SCTLR2_EL1

Yeoreum Yun posted 5 patches 1 month, 3 weeks ago
There is a newer version of this series
[PATCH v3 5/5] arm64: make the per-task SCTLR2_EL1
Posted by Yeoreum Yun 1 month, 3 weeks ago 
SCTLR2_EL1 register is optional starting from ARMv8.8/ARMv9.3,
and becomes mandatory from ARMv8.9/ARMv9.4
and serveral architectural feature are controled by bits in
these registers and some of bits could be configurable per task
not globally -- i.e) FEAT_CPA2 related field and etc.

For future usage of these fields, make the per-task SCTLR2_EL1.

Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
---
 arch/arm64/include/asm/processor.h | 5 +++++
 arch/arm64/kernel/process.c        | 9 +++++++++
 2 files changed, 14 insertions(+)

diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
index 61d62bfd5a7b..2c962816de70 100644
--- a/arch/arm64/include/asm/processor.h
+++ b/arch/arm64/include/asm/processor.h
@@ -184,6 +184,7 @@ struct thread_struct {
 	u64			mte_ctrl;
 #endif
 	u64			sctlr_user;
+	u64			sctlr2_user;
 	u64			svcr;
 	u64			tpidr2_el0;
 	u64			por_el0;
@@ -258,6 +259,9 @@ static inline void task_set_sve_vl_onexec(struct task_struct *task,
 	(SCTLR_ELx_ENIA | SCTLR_ELx_ENIB | SCTLR_ELx_ENDA | SCTLR_ELx_ENDB |   \
 	 SCTLR_EL1_TCF0_MASK)
 
+#define SCTLR2_USER_MASK	\
+	(SCTLR2_EL1_EnPACM0 | SCTLR2_EL1_CPTA0 | SCTLR2_EL1_CPTM0)
+
 static inline void arch_thread_struct_whitelist(unsigned long *offset,
 						unsigned long *size)
 {
@@ -370,6 +374,7 @@ struct task_struct;
 unsigned long __get_wchan(struct task_struct *p);
 
 void update_sctlr_el1(u64 sctlr);
+void update_sctlr2_el1(u64 sctlr2);
 
 /* Thread switching */
 extern struct task_struct *cpu_switch_to(struct task_struct *prev,
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 96482a1412c6..9191180c4875 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -698,6 +698,11 @@ void update_sctlr_el1(u64 sctlr)
 	isb();
 }
 
+void update_sctlr2_el1(u64 sctlr2)
+{
+	sysreg_clear_set_s(SYS_SCTLR2_EL1, SCTLR2_USER_MASK, sctlr2);
+}
+
 /*
  * Thread switching.
  */
@@ -737,6 +742,10 @@ struct task_struct *__switch_to(struct task_struct *prev,
 	if (prev->thread.sctlr_user != next->thread.sctlr_user)
 		update_sctlr_el1(next->thread.sctlr_user);
 
+	if (alternative_has_cap_unlikely(ARM64_HAS_SCTLR2) &&
+	    prev->thread.sctlr2_user != next->thread.sctlr2_user)
+		update_sctlr2_el1(next->thread.sctlr2_user);
+
 	/* the actual thread switch */
 	last = cpu_switch_to(prev, next);
 
-- 
LEVI:{C3F47F37-75D8-414A-A8BA-3980EC8A46D7}
Re: [PATCH v3 5/5] arm64: make the per-task SCTLR2_EL1
Posted by Dave Martin 1 month, 2 weeks ago 
Hi,

On Wed, Aug 13, 2025 at 01:01:18PM +0100, Yeoreum Yun wrote:
> SCTLR2_EL1 register is optional starting from ARMv8.8/ARMv9.3,
> and becomes mandatory from ARMv8.9/ARMv9.4
> and serveral architectural feature are controled by bits in
> these registers and some of bits could be configurable per task
> not globally -- i.e) FEAT_CPA2 related field and etc.
> 
> For future usage of these fields, make the per-task SCTLR2_EL1.

It is worth pointing out the impact of this: for platforms without
FEAT_SCTLR2 support, there is no functional change and minimal
performance overhead.

> Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
> ---
>  arch/arm64/include/asm/processor.h | 5 +++++
>  arch/arm64/kernel/process.c        | 9 +++++++++
>  2 files changed, 14 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
> index 61d62bfd5a7b..2c962816de70 100644
> --- a/arch/arm64/include/asm/processor.h
> +++ b/arch/arm64/include/asm/processor.h
> @@ -184,6 +184,7 @@ struct thread_struct {
>  	u64			mte_ctrl;
>  #endif
>  	u64			sctlr_user;
> +	u64			sctlr2_user;
>  	u64			svcr;
>  	u64			tpidr2_el0;
>  	u64			por_el0;
> @@ -258,6 +259,9 @@ static inline void task_set_sve_vl_onexec(struct task_struct *task,
>  	(SCTLR_ELx_ENIA | SCTLR_ELx_ENIB | SCTLR_ELx_ENDA | SCTLR_ELx_ENDB |   \
>  	 SCTLR_EL1_TCF0_MASK)
>  
> +#define SCTLR2_USER_MASK	\
> +	(SCTLR2_EL1_EnPACM0 | SCTLR2_EL1_CPTA0 | SCTLR2_EL1_CPTM0)
> +

The kernel doesn't know about any of these features, yet.

It's probably better to make this 0 for this patch series, and add bits
to this mask only when they are needed / used.

>  static inline void arch_thread_struct_whitelist(unsigned long *offset,
>  						unsigned long *size)
>  {
> @@ -370,6 +374,7 @@ struct task_struct;
>  unsigned long __get_wchan(struct task_struct *p);
>  
>  void update_sctlr_el1(u64 sctlr);
> +void update_sctlr2_el1(u64 sctlr2);

Is this function used outside process.c yet?  If not, you can drop this
declaration and [... below ...]
>  
>  /* Thread switching */
>  extern struct task_struct *cpu_switch_to(struct task_struct *prev,
> diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
> index 96482a1412c6..9191180c4875 100644
> --- a/arch/arm64/kernel/process.c
> +++ b/arch/arm64/kernel/process.c
> @@ -698,6 +698,11 @@ void update_sctlr_el1(u64 sctlr)
>  	isb();
>  }
>  
> +void update_sctlr2_el1(u64 sctlr2)

[...] make the function static here.


> +{
> +	sysreg_clear_set_s(SYS_SCTLR2_EL1, SCTLR2_USER_MASK, sctlr2);
> +}
> +
>  /*
>   * Thread switching.
>   */
> @@ -737,6 +742,10 @@ struct task_struct *__switch_to(struct task_struct *prev,
>  	if (prev->thread.sctlr_user != next->thread.sctlr_user)
>  		update_sctlr_el1(next->thread.sctlr_user);
>  
> +	if (alternative_has_cap_unlikely(ARM64_HAS_SCTLR2) &&
> +	    prev->thread.sctlr2_user != next->thread.sctlr2_user)
> +		update_sctlr2_el1(next->thread.sctlr2_user);
> +
>  	/* the actual thread switch */
>  	last = cpu_switch_to(prev, next);

[...]

Otherwise, I guess this looks OK.

Cheers
---Dave
Re: [PATCH v3 5/5] arm64: make the per-task SCTLR2_EL1
Posted by Yeoreum Yun 1 month, 2 weeks ago 
Hi Dave,

> On Wed, Aug 13, 2025 at 01:01:18PM +0100, Yeoreum Yun wrote:
> > SCTLR2_EL1 register is optional starting from ARMv8.8/ARMv9.3,
> > and becomes mandatory from ARMv8.9/ARMv9.4
> > and serveral architectural feature are controled by bits in
> > these registers and some of bits could be configurable per task
> > not globally -- i.e) FEAT_CPA2 related field and etc.
> >
> > For future usage of these fields, make the per-task SCTLR2_EL1.
>
> It is worth pointing out the impact of this: for platforms without
> FEAT_SCTLR2 support, there is no functional change and minimal
> performance overhead.

Thanks for your suggestion :)

>
> > Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
> > ---
> >  arch/arm64/include/asm/processor.h | 5 +++++
> >  arch/arm64/kernel/process.c        | 9 +++++++++
> >  2 files changed, 14 insertions(+)
> >
> > diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
> > index 61d62bfd5a7b..2c962816de70 100644
> > --- a/arch/arm64/include/asm/processor.h
> > +++ b/arch/arm64/include/asm/processor.h
> > @@ -184,6 +184,7 @@ struct thread_struct {
> >  	u64			mte_ctrl;
> >  #endif
> >  	u64			sctlr_user;
> > +	u64			sctlr2_user;
> >  	u64			svcr;
> >  	u64			tpidr2_el0;
> >  	u64			por_el0;
> > @@ -258,6 +259,9 @@ static inline void task_set_sve_vl_onexec(struct task_struct *task,
> >  	(SCTLR_ELx_ENIA | SCTLR_ELx_ENIB | SCTLR_ELx_ENDA | SCTLR_ELx_ENDB |   \
> >  	 SCTLR_EL1_TCF0_MASK)
> >
> > +#define SCTLR2_USER_MASK	\
> > +	(SCTLR2_EL1_EnPACM0 | SCTLR2_EL1_CPTA0 | SCTLR2_EL1_CPTM0)
> > +
>
> The kernel doesn't know about any of these features, yet.
>
> It's probably better to make this 0 for this patch series, and add bits
> to this mask only when they are needed / used.

I see. Thanks!

>
> >  static inline void arch_thread_struct_whitelist(unsigned long *offset,
> >  						unsigned long *size)
> >  {
> > @@ -370,6 +374,7 @@ struct task_struct;
> >  unsigned long __get_wchan(struct task_struct *p);
> >
> >  void update_sctlr_el1(u64 sctlr);
> > +void update_sctlr2_el1(u64 sctlr2);
>
> Is this function used outside process.c yet?  If not, you can drop this
> declaration and [... below ...]
> >
> >  /* Thread switching */
> >  extern struct task_struct *cpu_switch_to(struct task_struct *prev,
> > diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
> > index 96482a1412c6..9191180c4875 100644
> > --- a/arch/arm64/kernel/process.c
> > +++ b/arch/arm64/kernel/process.c
> > @@ -698,6 +698,11 @@ void update_sctlr_el1(u64 sctlr)
> >  	isb();
> >  }
> >
> > +void update_sctlr2_el1(u64 sctlr2)
>
> [...] make the function static here.

You're right. there's no usage anyware except here.
I'll change this.

Thanks!

>
>
> > +{
> > +	sysreg_clear_set_s(SYS_SCTLR2_EL1, SCTLR2_USER_MASK, sctlr2);
> > +}
> > +
> >  /*
> >   * Thread switching.
> >   */
> > @@ -737,6 +742,10 @@ struct task_struct *__switch_to(struct task_struct *prev,
> >  	if (prev->thread.sctlr_user != next->thread.sctlr_user)
> >  		update_sctlr_el1(next->thread.sctlr_user);
> >
> > +	if (alternative_has_cap_unlikely(ARM64_HAS_SCTLR2) &&
> > +	    prev->thread.sctlr2_user != next->thread.sctlr2_user)
> > +		update_sctlr2_el1(next->thread.sctlr2_user);
> > +
> >  	/* the actual thread switch */
> >  	last = cpu_switch_to(prev, next);
>
> [...]
>
> Otherwise, I guess this looks OK.
>
> Cheers
> ---Dave

--
Sincerely,
Yeoreum Yun

Patchew 2.1-devel-b67e4c2

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