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[2a02:3100:acb9:201:68d0:34d2:ad1a:175a]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49b95013d06sm370393515e9.12.2026.08.31.01.10.20 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Mon, 31 Aug 2026 01:10:21 -0700 (PDT) From: Karl Mehltretter To: Marc Zyngier , Oliver Upton , kvmarm@lists.linux.dev Cc: Karl Mehltretter , Fuad Tabba , Joey Gouly , Steffen Eiden , Suzuki K Poulose , Zenghui Yu , Catalin Marinas , Will Deacon , Paolo Bonzini , Shuah Khan , Eric Auger , Christoffer Dall , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: [PATCH v4 2/4] KVM: arm64: vgic-v3: Roll back assignments from the new region Date: Mon, 31 Aug 2026 10:10:02 +0200 Message-Id: <20260831081005.41346-3-kmehltretter@gmail.com> X-Mailer: git-send-email 2.39.5 (Apple Git-154) In-Reply-To: <20260831081005.41346-1-kmehltretter@gmail.com> References: <20260831081005.41346-1-kmehltretter@gmail.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit A failed REDIST_REGION write unregisters the redistributor iodevs of every vCPU processed before the failure. This includes vCPUs assigned to older regions. Their assignments remain cached, so a retry does not register the iodevs again. The vCPU whose registration fails has no assignment to roll back. For vCPUs processed earlier, limit rollback to those assigned to the new region. The region is removed on failure, so its free_index does not need restoring. Resetting assignments from older regions is unsafe because a vCPU can own one before kvm_for_each_vcpu() can see it. Rollback could then move free_index behind that live assignment. kvm_vgic_addr() holds slots_lock across the REDIST_REGION write. vCPU creation takes the same lock before assigning a redistributor. A concurrent vCPU cannot acquire an assignment from the new region before rollback completes. The lock also keeps rdreg valid across the config_lock drop required by MMIO-bus registration. Fixes: c011f4ea106b ("KVM: arm/arm64: Check vcpu redist base before registering an iodev") Cc: stable@vger.kernel.org Assisted-by: Codex:gpt-5.6-sol Signed-off-by: Karl Mehltretter --- arch/arm64/kvm/vgic/vgic-mmio-v3.c | 32 +++++++++++++++++++++++------- 1 file changed, 25 insertions(+), 7 deletions(-) diff --git a/arch/arm64/kvm/vgic/vgic-mmio-v3.c b/arch/arm64/kvm/vgic/vgic-mmio-v3.c index 22897ce64dbf..77aa8433701a 100644 --- a/arch/arm64/kvm/vgic/vgic-mmio-v3.c +++ b/arch/arm64/kvm/vgic/vgic-mmio-v3.c @@ -855,7 +855,25 @@ void vgic_unregister_redist_iodev(struct kvm_vcpu *vcpu) kvm_io_bus_unregister_dev(vcpu->kvm, KVM_MMIO_BUS, &rd_dev->dev); } -static int vgic_register_all_redist_iodevs(struct kvm *kvm) +static void vgic_rollback_redist_iodev(struct kvm_vcpu *vcpu, + struct vgic_redist_region *rdreg) +{ + struct vgic_cpu *vgic_cpu = &vcpu->arch.vgic_cpu; + + lockdep_assert_held(&vcpu->kvm->slots_lock); + + if (vgic_cpu->rdreg != rdreg) + return; + + vgic_unregister_redist_iodev(vcpu); + + guard(mutex)(&vcpu->kvm->arch.config_lock); + vgic_cpu->rdreg = NULL; + vgic_cpu->rd_iodev.base_addr = VGIC_ADDR_UNDEF; +} + +static int vgic_register_all_redist_iodevs(struct kvm *kvm, + struct vgic_redist_region *rdreg) { struct kvm_vcpu *vcpu; unsigned long c; @@ -870,12 +888,12 @@ static int vgic_register_all_redist_iodevs(struct kvm *kvm) } if (ret) { - /* The current c failed, so iterate over the previous ones. */ + /* Undo assignments made from the region being added. */ int i; for (i = 0; i < c; i++) { vcpu = kvm_get_vcpu(kvm, i); - vgic_unregister_redist_iodev(vcpu); + vgic_rollback_redist_iodev(vcpu, rdreg); } } @@ -984,10 +1002,13 @@ void vgic_v3_free_redist_region(struct kvm *kvm, struct vgic_redist_region *rdre int vgic_v3_set_redist_base(struct kvm *kvm, u32 index, u64 addr, u32 count) { + struct vgic_redist_region *rdreg; int ret; mutex_lock(&kvm->arch.config_lock); ret = vgic_v3_alloc_redist_region(kvm, index, addr, count); + if (!ret) + rdreg = vgic_v3_rdist_region_from_index(kvm, index); mutex_unlock(&kvm->arch.config_lock); if (ret) return ret; @@ -996,12 +1017,9 @@ int vgic_v3_set_redist_base(struct kvm *kvm, u32 index, u64 addr, u32 count) * Register iodevs for each existing VCPU. Adding more VCPUs * afterwards will register the iodevs when needed. */ - ret = vgic_register_all_redist_iodevs(kvm); + ret = vgic_register_all_redist_iodevs(kvm, rdreg); if (ret) { - struct vgic_redist_region *rdreg; - mutex_lock(&kvm->arch.config_lock); - rdreg = vgic_v3_rdist_region_from_index(kvm, index); vgic_v3_free_redist_region(kvm, rdreg); mutex_unlock(&kvm->arch.config_lock); return ret; -- 2.39.5 (Apple Git-154)