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Thu, 11 Jun 2026 02:09:49 -0700 (PDT) From: fuqiang wang To: Marc Zyngier , Oliver Upton , Zenghui Yu , linux-kernel@vger.kernel.org, kvmarm@lists.linux.dev Cc: dongxu zhang , wangfuqiang49 , fuqiang wang Subject: [PATCH 2/2] KVM: arm64: Skip unreset vCPUs in MPIDR lookup table Date: Thu, 11 Jun 2026 17:09:34 +0800 Message-ID: <20260611090934.84469-3-fuqiang.wng@gmail.com> X-Mailer: git-send-email 2.47.0 In-Reply-To: <20260611090934.84469-1-fuqiang.wng@gmail.com> References: <20260611090934.84469-1-fuqiang.wng@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit When a VM is created with CPU hotplug support, kvm_for_each_vcpu() can walk vCPUs that have not been reset yet. Their MPIDR_EL1 state is still zero, which aliases vCPU0 when populating the compressed MPIDR lookup table. As a result, cmpidr_to_idx[0] can be overwritten with the index of an unreset vCPU. A lookup for MPIDR 0 then returns the wrong vCPU, which can prevent interrupts targeting vCPU0 from being delivered correctly and make guest boot extremely slow. Skip vCPUs whose MPIDR_EL1 value does not have the RES1 bit set. Fixes: 5544750efd51 ("KVM: arm64: Build MPIDR to vcpu index cache at runtime") Signed-off-by: fuqiang wang --- arch/arm64/include/asm/kvm_emulate.h | 9 +++++++++ arch/arm64/kvm/arm.c | 10 ++++++++++ 2 files changed, 19 insertions(+) diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h index 5bf3d7e1d92c..8158e88aaa4e 100644 --- a/arch/arm64/include/asm/kvm_emulate.h +++ b/arch/arm64/include/asm/kvm_emulate.h @@ -506,6 +506,15 @@ static inline unsigned long kvm_vcpu_get_mpidr_aff(struct kvm_vcpu *vcpu) return __vcpu_sys_reg(vcpu, MPIDR_EL1) & MPIDR_HWID_BITMASK; } +/* + * Check if MPIDR matches hardware reset value. RES1 bits are set after reset, + * while a zero default indicates a vCPU that has not been reset. + */ +static inline bool kvm_vcpu_mpidr_is_reset(u64 val) +{ + return (val & MIDR_RES1_MASK) == MIDR_RES1_MASK; +} + static inline void kvm_vcpu_set_be(struct kvm_vcpu *vcpu) { if (vcpu_mode_is_32bit(vcpu)) { diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c index 3732ee9eb0d4..b47088201683 100644 --- a/arch/arm64/kvm/arm.c +++ b/arch/arm64/kvm/arm.c @@ -890,6 +890,16 @@ static void kvm_init_mpidr_data(struct kvm *kvm) u64 aff = kvm_vcpu_get_mpidr_aff(vcpu); u16 index = kvm_mpidr_index(data, aff); + /* + * In the CPU hot-plug scenario, the kvm_for_each_vcpu() macro + * iterates over all possible vcpus. For vcpus that are not + * reset, kvm_vcpu_get_mpidr_aff() returns 0, then the index + * computed by kvm_mpidr_index() will also be 0, thereby + * overwriting the original value of vcpu0. + */ + if (!kvm_vcpu_mpidr_is_reset(aff)) + continue; + data->cmpidr_to_idx[index] = c; } -- 2.47.0