path: root/virt
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authorMarc Zyngier <maz@kernel.org>2019-08-02 10:28:32 +0100
committerMarc Zyngier <maz@kernel.org>2019-08-05 15:36:46 +0100
commit5eeaf10eec394b28fad2c58f1f5c3a5da0e87d1c (patch)
treef7e6c05a259c908bae74fa2852b6d80d811e822d /virt
parentcdb2d3ee0436d74fa9092f2df46aaa6f9e03c969 (diff)
KVM: arm/arm64: Sync ICH_VMCR_EL2 back when about to block
Since commit commit 328e56647944 ("KVM: arm/arm64: vgic: Defer touching GICH_VMCR to vcpu_load/put"), we leave ICH_VMCR_EL2 (or its GICv2 equivalent) loaded as long as we can, only syncing it back when we're scheduled out. There is a small snag with that though: kvm_vgic_vcpu_pending_irq(), which is indirectly called from kvm_vcpu_check_block(), needs to evaluate the guest's view of ICC_PMR_EL1. At the point were we call kvm_vcpu_check_block(), the vcpu is still loaded, and whatever changes to PMR is not visible in memory until we do a vcpu_put(). Things go really south if the guest does the following: mov x0, #0 // or any small value masking interrupts msr ICC_PMR_EL1, x0 [vcpu preempted, then rescheduled, VMCR sampled] mov x0, #ff // allow all interrupts msr ICC_PMR_EL1, x0 wfi // traps to EL2, so samping of VMCR [interrupt arrives just after WFI] Here, the hypervisor's view of PMR is zero, while the guest has enabled its interrupts. kvm_vgic_vcpu_pending_irq() will then say that no interrupts are pending (despite an interrupt being received) and we'll block for no reason. If the guest doesn't have a periodic interrupt firing once it has blocked, it will stay there forever. To avoid this unfortuante situation, let's resync VMCR from kvm_arch_vcpu_blocking(), ensuring that a following kvm_vcpu_check_block() will observe the latest value of PMR. This has been found by booting an arm64 Linux guest with the pseudo NMI feature, and thus using interrupt priorities to mask interrupts instead of the usual PSTATE masking. Cc: stable@vger.kernel.org # 4.12 Fixes: 328e56647944 ("KVM: arm/arm64: vgic: Defer touching GICH_VMCR to vcpu_load/put") Signed-off-by: Marc Zyngier <maz@kernel.org>
Diffstat (limited to 'virt')
5 files changed, 38 insertions, 2 deletions
diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
index c704fa696184..482b20256fa8 100644
--- a/virt/kvm/arm/arm.c
+++ b/virt/kvm/arm/arm.c
@@ -323,6 +323,17 @@ int kvm_cpu_has_pending_timer(struct kvm_vcpu *vcpu)
void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu)
+ /*
+ * If we're about to block (most likely because we've just hit a
+ * WFI), we need to sync back the state of the GIC CPU interface
+ * so that we have the lastest PMR and group enables. This ensures
+ * that kvm_arch_vcpu_runnable has up-to-date data to decide
+ * whether we have pending interrupts.
+ */
+ preempt_disable();
+ kvm_vgic_vmcr_sync(vcpu);
+ preempt_enable();
diff --git a/virt/kvm/arm/vgic/vgic-v2.c b/virt/kvm/arm/vgic/vgic-v2.c
index 6dd5ad706c92..96aab77d0471 100644
--- a/virt/kvm/arm/vgic/vgic-v2.c
+++ b/virt/kvm/arm/vgic/vgic-v2.c
@@ -484,10 +484,17 @@ void vgic_v2_load(struct kvm_vcpu *vcpu)
kvm_vgic_global_state.vctrl_base + GICH_APR);
-void vgic_v2_put(struct kvm_vcpu *vcpu)
+void vgic_v2_vmcr_sync(struct kvm_vcpu *vcpu)
struct vgic_v2_cpu_if *cpu_if = &vcpu->arch.vgic_cpu.vgic_v2;
cpu_if->vgic_vmcr = readl_relaxed(kvm_vgic_global_state.vctrl_base + GICH_VMCR);
+void vgic_v2_put(struct kvm_vcpu *vcpu)
+ struct vgic_v2_cpu_if *cpu_if = &vcpu->arch.vgic_cpu.vgic_v2;
+ vgic_v2_vmcr_sync(vcpu);
cpu_if->vgic_apr = readl_relaxed(kvm_vgic_global_state.vctrl_base + GICH_APR);
diff --git a/virt/kvm/arm/vgic/vgic-v3.c b/virt/kvm/arm/vgic/vgic-v3.c
index c2c9ce009f63..0c653a1e5215 100644
--- a/virt/kvm/arm/vgic/vgic-v3.c
+++ b/virt/kvm/arm/vgic/vgic-v3.c
@@ -662,12 +662,17 @@ void vgic_v3_load(struct kvm_vcpu *vcpu)
-void vgic_v3_put(struct kvm_vcpu *vcpu)
+void vgic_v3_vmcr_sync(struct kvm_vcpu *vcpu)
struct vgic_v3_cpu_if *cpu_if = &vcpu->arch.vgic_cpu.vgic_v3;
if (likely(cpu_if->vgic_sre))
cpu_if->vgic_vmcr = kvm_call_hyp_ret(__vgic_v3_read_vmcr);
+void vgic_v3_put(struct kvm_vcpu *vcpu)
+ vgic_v3_vmcr_sync(vcpu);
kvm_call_hyp(__vgic_v3_save_aprs, vcpu);
diff --git a/virt/kvm/arm/vgic/vgic.c b/virt/kvm/arm/vgic/vgic.c
index 04786c8ec77e..13d4b38a94ec 100644
--- a/virt/kvm/arm/vgic/vgic.c
+++ b/virt/kvm/arm/vgic/vgic.c
@@ -919,6 +919,17 @@ void kvm_vgic_put(struct kvm_vcpu *vcpu)
+void kvm_vgic_vmcr_sync(struct kvm_vcpu *vcpu)
+ if (unlikely(!irqchip_in_kernel(vcpu->kvm)))
+ return;
+ if (kvm_vgic_global_state.type == VGIC_V2)
+ vgic_v2_vmcr_sync(vcpu);
+ else
+ vgic_v3_vmcr_sync(vcpu);
int kvm_vgic_vcpu_pending_irq(struct kvm_vcpu *vcpu)
struct vgic_cpu *vgic_cpu = &vcpu->arch.vgic_cpu;
diff --git a/virt/kvm/arm/vgic/vgic.h b/virt/kvm/arm/vgic/vgic.h
index 57205beaa981..11adbdac1d56 100644
--- a/virt/kvm/arm/vgic/vgic.h
+++ b/virt/kvm/arm/vgic/vgic.h
@@ -193,6 +193,7 @@ int vgic_register_dist_iodev(struct kvm *kvm, gpa_t dist_base_address,
void vgic_v2_init_lrs(void);
void vgic_v2_load(struct kvm_vcpu *vcpu);
void vgic_v2_put(struct kvm_vcpu *vcpu);
+void vgic_v2_vmcr_sync(struct kvm_vcpu *vcpu);
void vgic_v2_save_state(struct kvm_vcpu *vcpu);
void vgic_v2_restore_state(struct kvm_vcpu *vcpu);
@@ -223,6 +224,7 @@ bool vgic_v3_check_base(struct kvm *kvm);
void vgic_v3_load(struct kvm_vcpu *vcpu);
void vgic_v3_put(struct kvm_vcpu *vcpu);
+void vgic_v3_vmcr_sync(struct kvm_vcpu *vcpu);
bool vgic_has_its(struct kvm *kvm);
int kvm_vgic_register_its_device(void);

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