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Re: [PATCH v2 17/28] arm64/sve: Preserve SVE registers around kernel-mode NEON use
- 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, Catalin Marinas <catalin dot marinas at arm dot com>, Will Deacon <will dot deacon at arm dot com>, Ard Biesheuvel <ard dot biesheuvel at linaro dot org>, Szabolcs Nagy <szabolcs dot nagy at arm dot com>, Richard Sandiford <richard dot sandiford at arm dot com>, kvmarm at lists dot cs dot columbia dot edu, libc-alpha at sourceware dot org, linux-arch at vger dot kernel dot org
- Date: Thu, 14 Sep 2017 11:52:22 +0100
- Subject: Re: [PATCH v2 17/28] arm64/sve: Preserve SVE registers around kernel-mode NEON use
- Authentication-results: sourceware.org; auth=none
- References: <1504198860-12951-1-git-send-email-Dave.Martin@arm.com> <1504198860-12951-18-git-send-email-Dave.Martin@arm.com>
Dave Martin <Dave.Martin@arm.com> writes:
> Kernel-mode NEON will corrupt the SVE vector registers, due to the
> way they alias the FPSIMD vector registers in the hardware.
>
> This patch ensures that any live SVE register content for the task
> is saved by kernel_neon_begin(). The data will be restored in the
> usual way on return to userspace.
>
> Signed-off-by: Dave Martin <Dave.Martin@arm.com>
> Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
> ---
> arch/arm64/kernel/fpsimd.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
> index cea05a7..dd89acf 100644
> --- a/arch/arm64/kernel/fpsimd.c
> +++ b/arch/arm64/kernel/fpsimd.c
> @@ -744,8 +744,10 @@ void kernel_neon_begin(void)
> __this_cpu_write(kernel_neon_busy, true);
>
> /* Save unsaved task fpsimd state, if any: */
> - if (current->mm && !test_and_set_thread_flag(TIF_FOREIGN_FPSTATE))
> - fpsimd_save_state(¤t->thread.fpsimd_state);
> + if (current->mm) {
> + task_fpsimd_save();
> + set_thread_flag(TIF_FOREIGN_FPSTATE);
> + }
>
> /* Invalidate any task state remaining in the fpsimd regs: */
> __this_cpu_write(fpsimd_last_state, NULL);
--
Alex Bennée