[PATCH 3/3] KVM: arm64: vgic-its: Make updates to propbaser/pendbaser atomic
From: Christoffer Dall <hidden>
Date: 2016-08-03 16:13:25
Also in:
kvm, kvmarm
Subsystem:
kernel virtual machine (kvm), the rest · Maintainers:
Paolo Bonzini, Linus Torvalds
There are two problems with the current implementation of the MMIO handlers for the propbaser and pendbaser: First, the write to the value itself is not guaranteed to be an atomic 64-bit write so two concurrent writes to the structure field could be intermixed. Second, because we do a read-modify-update operation without any synchronization, if we have two 32-bit accesses to separate parts of the register, we can loose one of them. We can take the KVM mutex to synchronize accesses to these registers. Signed-off-by: Christoffer Dall <redacted> --- virt/kvm/arm/vgic/vgic-mmio-v3.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/virt/kvm/arm/vgic/vgic-mmio-v3.c b/virt/kvm/arm/vgic/vgic-mmio-v3.c
index ff668e0..e38b7a0 100644
--- a/virt/kvm/arm/vgic/vgic-mmio-v3.c
+++ b/virt/kvm/arm/vgic/vgic-mmio-v3.c@@ -306,16 +306,19 @@ static void vgic_mmio_write_propbase(struct kvm_vcpu *vcpu, { struct vgic_dist *dist = &vcpu->kvm->arch.vgic; struct vgic_cpu *vgic_cpu = &vcpu->arch.vgic_cpu; - u64 propbaser = dist->propbaser; + u64 propbaser; /* Storing a value with LPIs already enabled is undefined */ if (vgic_cpu->lpis_enabled) return; + mutex_lock(&vcpu->kvm->lock); + propbaser = dist->propbaser; propbaser = update_64bit_reg(propbaser, addr & 4, len, val); propbaser = vgic_sanitise_propbaser(propbaser); dist->propbaser = propbaser; + mutex_unlock(&vcpu->kvm->lock); } static unsigned long vgic_mmio_read_pendbase(struct kvm_vcpu *vcpu,
@@ -331,16 +334,19 @@ static void vgic_mmio_write_pendbase(struct kvm_vcpu *vcpu, unsigned long val) { struct vgic_cpu *vgic_cpu = &vcpu->arch.vgic_cpu; - u64 pendbaser = vgic_cpu->pendbaser; + u64 pendbaser; /* Storing a value with LPIs already enabled is undefined */ if (vgic_cpu->lpis_enabled) return; + mutex_lock(&vcpu->kvm->lock); + pendbaser = vgic_cpu->pendbaser; pendbaser = update_64bit_reg(pendbaser, addr & 4, len, val); pendbaser = vgic_sanitise_pendbaser(pendbaser); vgic_cpu->pendbaser = pendbaser; + mutex_unlock(&vcpu->kvm->lock); } /*
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2.9.0