linux-kernel - [PATCH v2 2/7] arm64: fpsimd: Make sure SVE setup is complete before SIMD is used

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Date:   Tue, 17 Dec 2019 18:33:57 +0000
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     linux-arm-kernel@...ts.infradead.org
Cc:     linux-kernel@...r.kernel.org, will@...nel.org, maz@...nel.org,
        mark.rutland@....com, dave.martin@....com, catalin.marinas@....com,
        ard.biesheuvel@...aro.org, christoffer.dall@....com,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Will Deacon <will.deacon@....com>
Subject: [PATCH v2 2/7] arm64: fpsimd: Make sure SVE setup is complete before SIMD is used

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@...aro.org>
Cc: Mark Rutland <mark.rutland@....com>
Cc: Will Deacon <will.deacon@....com>
Cc: Catalin Marinas <catalin.marinas@....com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@....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(-)

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 */
-- 
2.23.0