Re: [PATCH 12/27] arm64/sve: Support vector length resetting for new processes

[Dave Martin]

On Tue, Aug 22, 2017 at 05:22:11PM +0100, Alex Bennée wrote:
> 
> Dave Martin  writes:
> 
> > It's desirable to be able to reset the vector length to some sane
> > default for new processes, since the new binary and its libraries
> > processes may or may not be SVE-aware.
> >
> > This patch tracks the desired post-exec vector length (if any) in a
> > new thread member sve_vl_onexec, and adds a new thread flag
> > TIF_SVE_VL_INHERIT to control whether to inherit or reset the
> > vector length.  Currently these are inactive.  Subsequent patches
> > will provide the capability to configure them.
> >
> > Signed-off-by: Dave Martin 
> > ---
> >  arch/arm64/include/asm/processor.h   |  1 +
> >  arch/arm64/include/asm/thread_info.h |  1 +
> >  arch/arm64/kernel/fpsimd.c   | 13 +
> >  3 files changed, 15 insertions(+)
> >
> > diff --git a/arch/arm64/include/asm/processor.h 
> > b/arch/arm64/include/asm/processor.h
> > index 969feed..da8802a 100644
> > --- a/arch/arm64/include/asm/processor.h
> > +++ b/arch/arm64/include/asm/processor.h
> > @@ -87,6 +87,7 @@ struct thread_struct {
> > struct fpsimd_state fpsimd_state;
> > void*sve_state; /* SVE registers, if any */
> > u16 sve_vl; /* SVE vector length */
> > +   u16 sve_vl_onexec;  /* SVE vl after next
> > exec */
> 
> Inconsistent size usage here as well...

Agreed, the same history applies as for sve_vl.  I'll replace this with
an unsigned int.

[...]

Cheers
---Dave
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Re: [PATCH 12/27] arm64/sve: Support vector length resetting for new processes

[Alex Bennée]

Dave Martin  writes:

> It's desirable to be able to reset the vector length to some sane
> default for new processes, since the new binary and its libraries
> processes may or may not be SVE-aware.
>
> This patch tracks the desired post-exec vector length (if any) in a
> new thread member sve_vl_onexec, and adds a new thread flag
> TIF_SVE_VL_INHERIT to control whether to inherit or reset the
> vector length.  Currently these are inactive.  Subsequent patches
> will provide the capability to configure them.
>
> Signed-off-by: Dave Martin 
> ---
>  arch/arm64/include/asm/processor.h   |  1 +
>  arch/arm64/include/asm/thread_info.h |  1 +
>  arch/arm64/kernel/fpsimd.c   | 13 +
>  3 files changed, 15 insertions(+)
>
> diff --git a/arch/arm64/include/asm/processor.h 
> b/arch/arm64/include/asm/processor.h
> index 969feed..da8802a 100644
> --- a/arch/arm64/include/asm/processor.h
> +++ b/arch/arm64/include/asm/processor.h
> @@ -87,6 +87,7 @@ struct thread_struct {
>   struct fpsimd_state fpsimd_state;
>   void*sve_state; /* SVE registers, if any */
>   u16 sve_vl; /* SVE vector length */
> + u16 sve_vl_onexec;  /* SVE vl after next
> exec */

Inconsistent size usage here as well...

>   unsigned long   fault_address;  /* fault info */
>   unsigned long   fault_code; /* ESR_EL1 value */
>   struct debug_info   debug;  /* debugging */
> diff --git a/arch/arm64/include/asm/thread_info.h 
> b/arch/arm64/include/asm/thread_info.h
> index 1a4b30b..bf9c552 100644
> --- a/arch/arm64/include/asm/thread_info.h
> +++ b/arch/arm64/include/asm/thread_info.h
> @@ -97,6 +97,7 @@ struct thread_info {
>  #define TIF_SINGLESTEP   21
>  #define TIF_32BIT22  /* 32bit process */
>  #define TIF_SVE  23  /* Scalable Vector Extension in 
> use */
> +#define TIF_SVE_VL_INHERIT   24  /* Inherit sve_vl_onexec across exec */
>
>  #define _TIF_SIGPENDING  (1 << TIF_SIGPENDING)
>  #define _TIF_NEED_RESCHED(1 << TIF_NEED_RESCHED)
> diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
> index 37dd1b2..80ecb2d 100644
> --- a/arch/arm64/kernel/fpsimd.c
> +++ b/arch/arm64/kernel/fpsimd.c
> @@ -108,6 +108,9 @@ static void task_fpsimd_save(void);
>   */
>  static DEFINE_PER_CPU(struct fpsimd_state *, fpsimd_last_state);
>
> +/* Default VL for tasks that don't set it explicitly: */
> +static int sve_default_vl = -1;
> +
>  static void sve_free(struct task_struct *task)
>  {
>   kfree(task->thread.sve_state);
> @@ -392,6 +395,9 @@ void fpsimd_flush_thread(void)
>   clear_thread_flag(TIF_SVE);
>   sve_free(current);
>
> + current->thread.sve_vl = current->thread.sve_vl_onexec ?
> + current->thread.sve_vl_onexec : sve_default_vl;
> +
>   /*
>* User tasks must have a valid vector length set, but tasks
>* forked early (e.g., init) may not initially have one.
> @@ -401,6 +407,13 @@ void fpsimd_flush_thread(void)
>* If not, something went badly wrong.
>*/
>   BUG_ON(!sve_vl_valid(current->thread.sve_vl));
> +
> + /*
> +  * If the task is not set to inherit, ensure that the vector
> +  * length will be reset by a subsequent exec:
> +  */
> + if (!test_thread_flag(TIF_SVE_VL_INHERIT))
> + current->thread.sve_vl_onexec = 0;
>   }
>
>   set_thread_flag(TIF_FOREIGN_FPSTATE);


--
Alex Bennée
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