From e5cb94ba5f96d691d8885175d4696d6ae6bc5ec9 Mon Sep 17 00:00:00 2001 From: Marc Zyngier Date: Thu, 26 Feb 2026 08:22:32 +0000 Subject: [PATCH] arm64: Fix sampling the "stable" virtual counter in preemptible section MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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: 29cc0f3aa7c6 ("arm64: Force the use of CNTVCT_EL0 in __delay()") Reported-by: Ben Horgan Signed-off-by: Marc Zyngier Link: https://lore.kernel.org/r/aZw3EGs4rbQvbAzV@e134344.arm.com Tested-by: Ben Horgan Tested-by: André Draszik Signed-off-by: Will Deacon --- arch/arm64/lib/delay.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/arch/arm64/lib/delay.c b/arch/arm64/lib/delay.c index d02341303899..e278e060e78a 100644 --- a/arch/arm64/lib/delay.c +++ b/arch/arm64/lib/delay.c @@ -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) {