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From: Oliver Upton To: Marc Zyngier Cc: Raghavendra Rao Ananta , linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, stable@vger.kernel.org, syzbot Subject: Re: [PATCH] KVM: arm64: Mark the VM as dead for failed initializations Message-ID: References: <20241025221220.2985227-1-rananta@google.com> <87ttcztili.wl-maz@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87ttcztili.wl-maz@kernel.org> X-Migadu-Flow: FLOW_OUT On Sat, Oct 26, 2024 at 08:43:21AM +0100, Marc Zyngier wrote: > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h > index bf64fed9820e..c315bc1a4e9a 100644 > --- a/arch/arm64/include/asm/kvm_host.h > +++ b/arch/arm64/include/asm/kvm_host.h > @@ -74,8 +74,6 @@ enum kvm_mode kvm_get_mode(void); > static inline enum kvm_mode kvm_get_mode(void) { return KVM_MODE_NONE; }; > #endif > > -DECLARE_STATIC_KEY_FALSE(userspace_irqchip_in_use); > - > extern unsigned int __ro_after_init kvm_sve_max_vl; > extern unsigned int __ro_after_init kvm_host_sve_max_vl; > int __init kvm_arm_init_sve(void); > diff --git a/arch/arm64/kvm/arch_timer.c b/arch/arm64/kvm/arch_timer.c > index 879982b1cc73..1215df590418 100644 > --- a/arch/arm64/kvm/arch_timer.c > +++ b/arch/arm64/kvm/arch_timer.c > @@ -206,8 +206,7 @@ void get_timer_map(struct kvm_vcpu *vcpu, struct timer_map *map) > > static inline bool userspace_irqchip(struct kvm *kvm) > { > - return static_branch_unlikely(&userspace_irqchip_in_use) && > - unlikely(!irqchip_in_kernel(kvm)); > + return unlikely(!irqchip_in_kernel(kvm)); > } > > static void soft_timer_start(struct hrtimer *hrt, u64 ns) > diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c > index 48cafb65d6ac..70ff9a20ef3a 100644 > --- a/arch/arm64/kvm/arm.c > +++ b/arch/arm64/kvm/arm.c > @@ -69,7 +69,6 @@ DECLARE_KVM_NVHE_PER_CPU(struct kvm_cpu_context, kvm_hyp_ctxt); > static bool vgic_present, kvm_arm_initialised; > > static DEFINE_PER_CPU(unsigned char, kvm_hyp_initialized); > -DEFINE_STATIC_KEY_FALSE(userspace_irqchip_in_use); > > bool is_kvm_arm_initialised(void) > { > @@ -503,9 +502,6 @@ void kvm_arch_vcpu_postcreate(struct kvm_vcpu *vcpu) > > void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu) > { > - if (vcpu_has_run_once(vcpu) && unlikely(!irqchip_in_kernel(vcpu->kvm))) > - static_branch_dec(&userspace_irqchip_in_use); > - > kvm_mmu_free_memory_cache(&vcpu->arch.mmu_page_cache); > kvm_timer_vcpu_terminate(vcpu); > kvm_pmu_vcpu_destroy(vcpu); > @@ -848,14 +844,6 @@ int kvm_arch_vcpu_run_pid_change(struct kvm_vcpu *vcpu) > return ret; > } > > - if (!irqchip_in_kernel(kvm)) { > - /* > - * Tell the rest of the code that there are userspace irqchip > - * VMs in the wild. > - */ > - static_branch_inc(&userspace_irqchip_in_use); > - } > - > /* > * Initialize traps for protected VMs. > * NOTE: Move to run in EL2 directly, rather than via a hypercall, once > @@ -1077,7 +1065,7 @@ static bool kvm_vcpu_exit_request(struct kvm_vcpu *vcpu, int *ret) > * state gets updated in kvm_timer_update_run and > * kvm_pmu_update_run below). > */ > - if (static_branch_unlikely(&userspace_irqchip_in_use)) { > + if (unlikely(!irqchip_in_kernel(vcpu->kvm))) { > if (kvm_timer_should_notify_user(vcpu) || > kvm_pmu_should_notify_user(vcpu)) { > *ret = -EINTR; > @@ -1199,7 +1187,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu) > vcpu->mode = OUTSIDE_GUEST_MODE; > isb(); /* Ensure work in x_flush_hwstate is committed */ > kvm_pmu_sync_hwstate(vcpu); > - if (static_branch_unlikely(&userspace_irqchip_in_use)) > + if (unlikely(!irqchip_in_kernel(vcpu->kvm))) > kvm_timer_sync_user(vcpu); > kvm_vgic_sync_hwstate(vcpu); > local_irq_enable(); > @@ -1245,7 +1233,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu) > * we don't want vtimer interrupts to race with syncing the > * timer virtual interrupt state. > */ > - if (static_branch_unlikely(&userspace_irqchip_in_use)) > + if (unlikely(!irqchip_in_kernel(vcpu->kvm))) > kvm_timer_sync_user(vcpu); > > kvm_arch_vcpu_ctxsync_fp(vcpu); > > I think this would fix the problem you're seeing without changing the > userspace view of an erroneous configuration. It would also pave the > way for the complete removal of the interrupt notification to > userspace, which I claim has no user and is just a shit idea. Yeah, looks like this ought to get it done. Even with a fix for this particular issue I do wonder if we should categorically harden against late initialization failures and un-init the vCPU (or bug VM, where necessary) to avoid dealing with half-baked vCPUs/VMs across our UAPI surfaces. A sane userspace will probably crash when KVM_RUN returns EINVAL anyway. -- Thanks, Oliver