[PATCH v4 17/28] arm64/sve: Preserve SVE registers around kernel-mode NEON use

Dave Martin
2017-10-27T10:50:29Z

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>
---
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 703e9d7..d5108e8 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -884,8 +884,10 @@ 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);
--
2.1.4

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