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

• From: Alex Bennée <alex dot bennee at linaro dot org>
• To: Dave Martin <Dave dot Martin at arm dot com>
• Cc: linux-arm-kernel at lists dot infradead dot org, linux-arch at vger dot kernel dot org, libc-alpha at sourceware dot org, Ard Biesheuvel <ard dot biesheuvel at linaro dot org>, Szabolcs Nagy <szabolcs dot nagy at arm dot com>, Catalin Marinas <catalin dot marinas at arm dot com>, Will Deacon <will dot deacon at arm dot com>, Richard Sandiford <richard dot sandiford at arm dot com>, kvmarm at lists dot cs dot columbia dot edu
• Date: Tue, 22 Aug 2017 17:22:11 +0100
• Subject: Re: [PATCH 12/27] arm64/sve: Support vector length resetting for new processes
• Authentication-results: sourceware.org; auth=none
• References: <1502280338-23002-1-git-send-email-Dave.Martin@arm.com> <1502280338-23002-13-git-send-email-Dave.Martin@arm.com>

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_statefpsimd_state;>  void*sve_state;/* SVE registers, if any */>  u16sve_vl;/* SVE vector length */> +u16sve_vl_onexec;/* SVE vl after next> exec */Inconsistent size usage here as well...>  unsigned longfault_address;/* fault info */>  unsigned longfault_code;/* ESR_EL1 value */>  struct debug_infodebug;/* 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_SINGLESTEP21>  #define TIF_32BIT22/* 32bit process */>  #define TIF_SVE23/* Scalable Vector Extension in use */> +#define TIF_SVE_VL_INHERIT24/* 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

• Follow-Ups:
  • Re: [PATCH 12/27] arm64/sve: Support vector length resetting for new processes
    • From: Dave Martin

• References:
  • [PATCH 00/27] ARM Scalable Vector Extension (SVE)
    • From: Dave Martin
  • [PATCH 12/27] arm64/sve: Support vector length resetting for new processes
    • From: Dave Martin