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Fri, 11 Jul 2025 09:36:05 +0100 Date: Fri, 11 Jul 2025 09:36:04 +0100 Message-ID: <86h5zj9laj.wl-maz@kernel.org> From: Marc Zyngier To: Arnd Bergmann Cc: Oliver Upton , Catalin Marinas , Will Deacon , Arnd Bergmann , Joey Gouly , Suzuki K Poulose , Zenghui Yu , Mark Brown , James Morse , Sebastian Ott , linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org Subject: Re: [PATCH] KVM: arm64: fix u64_replace_bits() usage In-Reply-To: <20250711072752.2781647-1-arnd@kernel.org> References: <20250711072752.2781647-1-arnd@kernel.org> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/30.1 (aarch64-unknown-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: arnd@kernel.org, oliver.upton@linux.dev, catalin.marinas@arm.com, will@kernel.org, arnd@arndb.de, joey.gouly@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, broonie@kernel.org, james.morse@arm.com, sebott@redhat.com, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250711_013610_388993_30DDA5DA X-CRM114-Status: GOOD ( 23.08 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, 11 Jul 2025 08:27:47 +0100, Arnd Bergmann wrote: > > From: Arnd Bergmann > > 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 > --- > 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); This is only in -next, right? Because I have a fix for this already queued for 6.16, as per [1]. Thanks, M. [1] https://lore.kernel.org/r/20250709093808.920284-2-ben.horgan@arm.com -- Without deviation from the norm, progress is not possible.