[v2,2/7] arm64: fpsimd: Make sure SVE setup is complete before SIMD is used

Message ID 20191217183402.2259904-3-suzuki.poulose@arm.com
State Accepted
Commit 0cd82feb017e282b29e725801b7c90da69316734
Headers show
Series
  • arm64: Fix support for no FP/SIMD
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Commit Message

Suzuki Kuruppassery Poulose Dec. 17, 2019, 6:33 p.m.
In-kernel users of NEON rely on may_use_simd() to check if the SIMD
can be used. However, we must initialize the SVE before SIMD can
be used. Add a sanity check to make sure that we have completed the
SVE setup before anyone uses the SIMD.

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>

---
Discussion here : https://lkml.kernel.org/r/20191014145204.GS27757@arm.com
---
 arch/arm64/include/asm/simd.h | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

-- 
2.23.0

Patch

diff --git a/arch/arm64/include/asm/simd.h b/arch/arm64/include/asm/simd.h
index 7434844036d3..afce6409be51 100644
--- a/arch/arm64/include/asm/simd.h
+++ b/arch/arm64/include/asm/simd.h
@@ -26,6 +26,8 @@  DECLARE_PER_CPU(bool, fpsimd_context_busy);
 static __must_check inline bool may_use_simd(void)
 {
 	/*
+	 * We must make sure that the SVE has been initialized properly
+	 * before using the SIMD in kernel.
 	 * fpsimd_context_busy is only set while preemption is disabled,
 	 * and is clear whenever preemption is enabled. Since
 	 * this_cpu_read() is atomic w.r.t. preemption, fpsimd_context_busy
@@ -33,8 +35,10 @@  static __must_check inline bool may_use_simd(void)
 	 * migrated, and if it's clear we cannot be migrated to a CPU
 	 * where it is set.
 	 */
-	return !in_irq() && !irqs_disabled() && !in_nmi() &&
-		!this_cpu_read(fpsimd_context_busy);
+	return system_capabilities_finalized() &&
+	       system_supports_fpsimd() &&
+	       !in_irq() && !irqs_disabled() && !in_nmi() &&
+	       !this_cpu_read(fpsimd_context_busy);
 }
 
 #else /* ! CONFIG_KERNEL_MODE_NEON */