linux-kernel - [PATCH] KVM: arm64: fix u64_replace

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Message-Id: <20250711072752.2781647-1-arnd@kernel.org>
Date: Fri, 11 Jul 2025 09:27:47 +0200
From: Arnd Bergmann <arnd@...nel.org>
To: Marc Zyngier <maz@...nel.org>,
	Oliver Upton <oliver.upton@...ux.dev>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>
Cc: Arnd Bergmann <arnd@...db.de>,
	Joey Gouly <joey.gouly@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Zenghui Yu <yuzenghui@...wei.com>,
	Mark Brown <broonie@...nel.org>,
	James Morse <james.morse@....com>,
	Sebastian Ott <sebott@...hat.com>,
	linux-arm-kernel@...ts.infradead.org,
	kvmarm@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: [PATCH] KVM: arm64: fix u64_replace_bits() usage

From: Arnd Bergmann <arnd@...db.de>

u64_replace_bits() returns a modified word but does not actually modify
its argument, as pointed out by this new warning:

arch/arm64/kvm/sys_regs.c: In function 'access_mdcr':
arch/arm64/kvm/sys_regs.c:2654:17: error: ignoring return value of 'u64_replace_bits' declared with attribute 'warn_unused_result' [-Werror=unused-result]
 2654 |                 u64_replace_bits(val, hpmn, MDCR_EL2_HPMN);

The intention here must have been to update 'val', so do that instead.

Fixes: efff9dd2fee7 ("KVM: arm64: Handle out-of-bound write to MDCR_EL2.HPMN")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 arch/arm64/kvm/sys_regs.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 33aa4f5071b8..793fb19bebd6 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -2651,7 +2651,7 @@ static bool access_mdcr(struct kvm_vcpu *vcpu,
 	 */
 	if (hpmn > vcpu->kvm->arch.nr_pmu_counters) {
 		hpmn = vcpu->kvm->arch.nr_pmu_counters;
-		u64_replace_bits(val, hpmn, MDCR_EL2_HPMN);
+		val = u64_replace_bits(val, hpmn, MDCR_EL2_HPMN);
 	}
 
 	__vcpu_assign_sys_reg(vcpu, MDCR_EL2, val);
-- 
2.39.5