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Thu, 11 Jun 2026 07:40:56 -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 v2 2/2] KVM: arm64: Skip unreset vCPUs in MPIDR lookup table Date: Thu, 11 Jun 2026 22:40:42 +0800 Message-ID: <20260611144042.97981-3-fuqiang.wng@gmail.com> X-Mailer: git-send-email 2.47.0 In-Reply-To: <20260611144042.97981-1-fuqiang.wng@gmail.com> References: <20260611144042.97981-1-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 | 14 ++++++++++++-- 2 files changed, 21 insertions(+), 2 deletions(-) diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h index 5bf3d7e1d92c..3d2f0a8b040d 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 vCPU MPIDR_EL1 has been reset. MPIDR_EL1.bit[31] is RES1 + * and set during reset; a zero value indicates the vCPU is unreset. + */ +static inline bool kvm_vcpu_mpidr_is_reset(struct kvm_vcpu *vcpu) +{ + return !!(__vcpu_sys_reg(vcpu, MPIDR_EL1) & MPIDR_RES1_BITMASK); +} + 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..fccfa97370df 100644 --- a/arch/arm64/kvm/arm.c +++ b/arch/arm64/kvm/arm.c @@ -887,8 +887,18 @@ static void kvm_init_mpidr_data(struct kvm *kvm) data->mpidr_mask = mask; kvm_for_each_vcpu(c, vcpu, kvm) { - u64 aff = kvm_vcpu_get_mpidr_aff(vcpu); - u16 index = kvm_mpidr_index(data, aff); + u64 aff; + u16 index; + + /* + * Skip vCPUs that haven't been reset yet; their MPIDR_EL1 is + * zero. + */ + if (!kvm_vcpu_mpidr_is_reset(vcpu)) + continue; + + aff = kvm_vcpu_get_mpidr_aff(vcpu); + index = kvm_mpidr_index(data, aff); data->cmpidr_to_idx[index] = c; } -- 2.47.0