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arm64/fpsimd: signal: Simplify preserve_tpidr2_context()

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During a context-switch, tls_thread_switch() reads and writes a task's
thread_struct::tpidr2_el0 field. Other code shouldn't access this field
for an active task, as such accesses would form a data-race with a
concurrent context-switch.

The usage in preserve_tpidr2_context() is suspicious, but benign as any
race with a context switch will write the same value back to
current->thread.tpidr2_el0.

Make this clearer and match restore_tpidr2_context() by using a
temporary variable instead, avoiding the (benign) data-race.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20250409164010.3480271-14-mark.rutland@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
Mark Rutland 2025-04-09 17:40:10 +01:00 committed by Catalin Marinas
parent 929fa99b12
commit 2fe2b96c38
1 changed files with 2 additions and 3 deletions
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5
arch/arm64/kernel/signal.c
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@ -478,13 +478,12 @@ extern int preserve_sve_context(void __user *ctx);
static int preserve_tpidr2_context(struct tpidr2_context __user *ctx)
{
u64 tpidr2_el0 = read_sysreg_s(SYS_TPIDR2_EL0);
int err = 0;
current->thread.tpidr2_el0 = read_sysreg_s(SYS_TPIDR2_EL0);
__put_user_error(TPIDR2_MAGIC, &ctx->head.magic, err);
__put_user_error(sizeof(*ctx), &ctx->head.size, err);
__put_user_error(current->thread.tpidr2_el0, &ctx->tpidr2, err);
__put_user_error(tpidr2_el0, &ctx->tpidr2, err);
return err;
}