Re: [PATCH v2 20/28] arm64/sve: Add prctl controls for userspace vector length management

Alex Bennée
2017-09-14T13:02:50Z

Dave Martin <Dave.Martin@arm.com> writes:

> This patch adds two arm64-specific prctls, to permit userspace to
> control its vector length:
>
> * PR_SVE_SET_VL: set the thread's SVE vector length and vector
> length inheritance mode.
>
> * PR_SVE_GET_VL: get the same information.
>
> Although these calls shadow instruction set features in the SVE
> architecture, these prctls provide additional control: the vector
> length inheritance mode is Linux-specific and nothing to do with
> the architecture, and the architecture does not permit EL0 to set
> its own vector length directly. Both can be used in portable tools
> without requiring the use of SVE instructions.
>
> Signed-off-by: Dave Martin <Dave.Martin@arm.com>

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>

> ---
> arch/arm64/include/asm/fpsimd.h | 14 ++++++++++++
> arch/arm64/include/asm/processor.h | 4 ++++
> arch/arm64/kernel/fpsimd.c | 46 ++++++++++++++++++++++++++++++++++++++
> include/uapi/linux/prctl.h | 4 ++++
> kernel/sys.c | 12 ++++++++++
> 5 files changed, 80 insertions(+)
>
> diff --git a/arch/arm64/include/asm/fpsimd.h b/arch/arm64/include/asm/fpsimd.h
> index 2723cca..d084968 100644
> --- a/arch/arm64/include/asm/fpsimd.h
> +++ b/arch/arm64/include/asm/fpsimd.h
> @@ -17,6 +17,7 @@
> #define __ASM_FP_H
>
> #include <asm/ptrace.h>
> +#include <asm/errno.h>
>
> #ifndef __ASSEMBLY__
>
> @@ -99,6 +100,9 @@ extern void sve_sync_from_fpsimd_zeropad(struct task_struct *task);
> extern int sve_set_vector_length(struct task_struct *task,
> unsigned long vl, unsigned long flags);
>
> +extern int sve_set_current_vl(unsigned long arg);
> +extern int sve_get_current_vl(void);
> +
> extern void __init sve_init_vq_map(void);
> extern void sve_update_vq_map(void);
> extern int sve_verify_vq_map(void);
> @@ -114,6 +118,16 @@ static void __maybe_unused sve_sync_to_fpsimd(struct task_struct *task) { }
> static void __maybe_unused sve_sync_from_fpsimd_zeropad(
> struct task_struct *task) { }
>
> +static int __maybe_unused sve_set_current_vl(unsigned long arg)
> +{
> + return -EINVAL;
> +}
> +
> +static int __maybe_unused sve_get_current_vl(void)
> +{
> + return -EINVAL;
> +}
> +
> static void __maybe_unused sve_init_vq_map(void) { }
> static void __maybe_unused sve_update_vq_map(void) { }
> static int __maybe_unused sve_verify_vq_map(void) { return 0; }
> diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
> index 3faceac..df66452 100644
> --- a/arch/arm64/include/asm/processor.h
> +++ b/arch/arm64/include/asm/processor.h
> @@ -197,4 +197,8 @@ static inline void spin_lock_prefetch(const void *ptr)
> int cpu_enable_pan(void *__unused);
> int cpu_enable_cache_maint_trap(void *__unused);
>
> +/* Userspace interface for PR_SVE_{SET,GET}_VL prctl()s: */
> +#define SVE_SET_VL(arg) sve_set_current_vl(arg)
> +#define SVE_GET_VL() sve_get_current_vl()
> +
> #endif /* __ASM_PROCESSOR_H */
> diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
> index 361c019..42e8331 100644
> --- a/arch/arm64/kernel/fpsimd.c
> +++ b/arch/arm64/kernel/fpsimd.c
> @@ -27,6 +27,7 @@
> #include <linux/kernel.h>
> #include <linux/init.h>
> #include <linux/percpu.h>
> +#include <linux/prctl.h>
> #include <linux/preempt.h>
> #include <linux/prctl.h>
> #include <linux/ptrace.h>
> @@ -420,6 +421,51 @@ int sve_set_vector_length(struct task_struct *task,
> return 0;
> }
>
> +/*
> + * Encode the current vector length and flags for return.
> + * This is only required for prctl(): ptrace has separate fields
> + */
> +static int sve_prctl_status(void)
> +{
> + int ret = current->thread.sve_vl;
> +
> + if (test_thread_flag(TIF_SVE_VL_INHERIT))
> + ret |= PR_SVE_VL_INHERIT;
> +
> + return ret;
> +}
> +
> +/* PR_SVE_SET_VL */
> +int sve_set_current_vl(unsigned long arg)
> +{
> + unsigned long vl, flags;
> + int ret;
> +
> + vl = arg & PR_SVE_VL_LEN_MASK;
> + flags = arg & ~vl;
> +
> + if (!system_supports_sve())
> + return -EINVAL;
> +
> + preempt_disable();
> + ret = sve_set_vector_length(current, vl, flags);
> + preempt_enable();
> +
> + if (ret)
> + return ret;
> +
> + return sve_prctl_status();
> +}
> +
> +/* PR_SVE_GET_VL */
> +int sve_get_current_vl(void)
> +{
> + if (!system_supports_sve())
> + return -EINVAL;
> +
> + return sve_prctl_status();
> +}
> +
> static unsigned long *sve_alloc_vq_map(void)
> {
> return kzalloc(BITS_TO_LONGS(SVE_VQ_MAX) * sizeof(unsigned long),
> diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
> index 1b64901..1ef9370 100644
> --- a/include/uapi/linux/prctl.h
> +++ b/include/uapi/linux/prctl.h
> @@ -198,7 +198,11 @@ struct prctl_mm_map {
> # define PR_CAP_AMBIENT_CLEAR_ALL 4
>
> /* arm64 Scalable Vector Extension controls */
> +/* Flag values must be kept in sync with ptrace NT_ARM_SVE interface */
> +#define PR_SVE_SET_VL 48 /* set task vector length */
> # define PR_SVE_SET_VL_ONEXEC (1 << 18) /* defer effect until exec */
> +#define PR_SVE_GET_VL 49 /* get task vector length */
> +/* Bits common to PR_SVE_SET_VL and PR_SVE_GET_VL */
> # define PR_SVE_VL_LEN_MASK 0xffff
> # define PR_SVE_VL_INHERIT (1 << 17) /* inherit across exec */
>
> diff --git a/kernel/sys.c b/kernel/sys.c
> index 2855ee7..f8215a6 100644
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -110,6 +110,12 @@
> #ifndef SET_FP_MODE
> # define SET_FP_MODE(a,b) (-EINVAL)
> #endif
> +#ifndef SVE_SET_VL
> +# define SVE_SET_VL(a) (-EINVAL)
> +#endif
> +#ifndef SVE_GET_VL
> +# define SVE_GET_VL() (-EINVAL)
> +#endif
>
> /*
> * this is where the system-wide overflow UID and GID are defined, for
> @@ -2389,6 +2395,12 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
> case PR_GET_FP_MODE:
> error = GET_FP_MODE(me);
> break;
> + case PR_SVE_SET_VL:
> + error = SVE_SET_VL(arg2);
> + break;
> + case PR_SVE_GET_VL:
> + error = SVE_GET_VL();
> + break;
> default:
> error = -EINVAL;
> break;