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Subject[PATCH v2 2/7] arm64: fpsimd: Make sure SVE setup is complete before SIMD is used
Date
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(-)

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
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