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

From: Arnd Bergmann <arnd@arndb.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@arndb.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



             reply	other threads:[~2025-07-11  7:45 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-07-11  7:27 Arnd Bergmann [this message]
2025-07-11  8:02 ` [PATCH] KVM: arm64: fix u64_replace_bits() usage Zenghui Yu
2025-07-11  8:36 ` Marc Zyngier
2025-07-11  8:44   ` Arnd Bergmann
2025-07-11  8:53     ` Marc Zyngier
2025-07-11  9:13       ` Mark Brown

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