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

Alex Bennée
2017-08-22T16:22:11Z

Dave Martin <Dave.Martin@arm.com> 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 <Dave.Martin@arm.com>
> ---
> 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_32BIT 22 /* 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