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arm64: Fix sampling the "stable" virtual counter in preemptible section

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Ben reports that when running with CONFIG_DEBUG_PREEMPT, using
__arch_counter_get_cntvct_stable() results in well deserves warnings,
as we access a per-CPU variable without preemption disabled.

Fix the issue by disabling preemption on reading the counter. We can
probably do a lot better by not disabling preemption on systems that
do not require horrible workarounds to return a valid counter value,
but this plugs the issue for the time being.

Fixes: 29cc0f3aa7 ("arm64: Force the use of CNTVCT_EL0 in __delay()")
Reported-by: Ben Horgan <ben.horgan@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/aZw3EGs4rbQvbAzV@e134344.arm.com
Tested-by: Ben Horgan <ben.horgan@arm.com>
Tested-by: André Draszik <andre.draszik@linaro.org>
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Marc Zyngier 2026-02-26 08:22:32 +00:00 • committed by Will Deacon
parent a8f78680ee
commit e5cb94ba5f
1 changed files with 5 additions and 1 deletions
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6
arch/arm64/lib/delay.c
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@ -32,7 +32,11 @@ static inline unsigned long xloops_to_cycles(unsigned long xloops)
* Note that userspace cannot change the offset behind our back either,
* as the vcpu mutex is held as long as KVM_RUN is in progress.
*/
#define __delay_cycles() __arch_counter_get_cntvct_stable()
static cycles_t notrace __delay_cycles(void)
{
guard(preempt_notrace)();
return __arch_counter_get_cntvct_stable();
}
void __delay(unsigned long cycles)
{