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[PATCH 16/27] arm64/sve: Preserve SVE registers around kernel-mode NEON use

• From: Dave Martin <Dave dot Martin at arm dot com>
• To: linux-arm-kernel at lists dot infradead dot org
• Cc: 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: Wed, 9 Aug 2017 13:05:22 +0100
• Subject: [PATCH 16/27] arm64/sve: Preserve SVE registers around kernel-mode NEON use
• Authentication-results: sourceware.org; auth=none
• References: <1502280338-23002-1-git-send-email-Dave.Martin@arm.com>

Kernel-mode NEON will corrupt the SVE vector registers, due to theway they alias the FPSIMD vector registers in the hardware.This patch ensures that any live SVE register content for the taskis saved by kernel_neon_begin().  The data will be restored in theusual way on return to userspace.Signed-off-by: Dave Martin <Dave.Martin@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.cindex 955c873..b7fb836 100644--- a/arch/arm64/kernel/fpsimd.c+++ b/arch/arm64/kernel/fpsimd.c@@ -758,8 +758,10 @@ 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

• Follow-Ups:
  • Re: [PATCH 16/27] arm64/sve: Preserve SVE registers around kernel-mode NEON use
    • From: Ard Biesheuvel

• References:
  • [PATCH 00/27] ARM Scalable Vector Extension (SVE)
    • From: Dave Martin