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KVM: arm64: vgic-its: Make updates to propbaser/pendbaser atomic

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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.

By using the atomic cmpxchg64 we should cover both issues above.

Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
This commit is contained in:
Christoffer Dall 2016-08-03 18:03:44 +02:00
parent 2cccbb368a
commit d9ae449b3d
1 changed files with 16 additions and 10 deletions
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26
virt/kvm/arm/vgic/vgic-mmio-v3.c
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@ -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 old_propbaser, propbaser;
/* Storing a value with LPIs already enabled is undefined */
if (vgic_cpu->lpis_enabled)
return;
propbaser = update_64bit_reg(propbaser, addr & 4, len, val);
propbaser = vgic_sanitise_propbaser(propbaser);
dist->propbaser = propbaser;
do {
old_propbaser = dist->propbaser;
propbaser = old_propbaser;
propbaser = update_64bit_reg(propbaser, addr & 4, len, val);
propbaser = vgic_sanitise_propbaser(propbaser);
} while (cmpxchg64(&dist->propbaser, old_propbaser,
propbaser) != old_propbaser);
}
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 old_pendbaser, pendbaser;
/* Storing a value with LPIs already enabled is undefined */
if (vgic_cpu->lpis_enabled)
return;
pendbaser = update_64bit_reg(pendbaser, addr & 4, len, val);
pendbaser = vgic_sanitise_pendbaser(pendbaser);
vgic_cpu->pendbaser = pendbaser;
do {
old_pendbaser = vgic_cpu->pendbaser;
pendbaser = old_pendbaser;
pendbaser = update_64bit_reg(pendbaser, addr & 4, len, val);
pendbaser = vgic_sanitise_pendbaser(pendbaser);
} while (cmpxchg64(&vgic_cpu->pendbaser, old_pendbaser,
pendbaser) != old_pendbaser);
}
/*