Patchwork [v3,17/28] arm64/sve: Preserve SVE registers around kernel-mode NEON use

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Submitter Dave Martin
Date Oct. 10, 2017, 6:38 p.m.
Message ID <1507660725-7986-18-git-send-email-Dave.Martin@arm.com>
Download mbox | patch
Permalink /patch/23448/
State New
Headers show

Comments

Dave Martin - Oct. 10, 2017, 6:38 p.m.
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(-)
Catalin Marinas - Oct. 12, 2017, 10:15 a.m.
On Tue, Oct 10, 2017 at 07:38:34PM +0100, Dave P Martin wrote:
> 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>

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>

Patch

diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index 5673f50..b1d383a 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -909,8 +909,10 @@  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(&current->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);