linux-kernel - [PATCH v3 2/7] arm64: fpsimd: Make sure SVE setup is complete before SIMD is used

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Message-Id: <20200113233023.928028-3-suzuki.poulose@arm.com>
Date:   Mon, 13 Jan 2020 23:30:18 +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,
        catalin.marinas@....com, ard.biesheuvel@...aro.org,
        mark.rutland@....com, Suzuki K Poulose <suzuki.poulose@....com>
Subject: [PATCH v3 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@...nel.org>
Cc: Catalin Marinas <catalin.marinas@....com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
---
Changes since v2:
  - Add WARN_ON() in may_use_simd() if invoked before caps
    are finalized()
---
 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..89cba2622b79 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 !WARN_ON(!system_capabilities_finalized()) &&
+	       system_supports_fpsimd() &&
+	       !in_irq() && !irqs_disabled() && !in_nmi() &&
+	       !this_cpu_read(fpsimd_context_busy);
 }
 
 #else /* ! CONFIG_KERNEL_MODE_NEON */
-- 
2.24.1