Commit 1bd3f936 authored Oct 31, 2017 by Dave Martin Committed by Will Deacon Nov 03, 2017

arm64/sve: Preserve SVE registers around kernel-mode NEON use



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>
Signed-off-by: Will Deacon <will.deacon@arm.com>

parent 2e0f2478

arch/arm64/kernel/fpsimd.c

+4 −2

Original line number	Diff line number	Diff line
		@@ -886,8 +886,10 @@ 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);