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Commit d9ae449b authored by Christoffer Dall's avatar Christoffer Dall
Browse files

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



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: default avatarAndre Przywara <andre.przywara@arm.com>
Signed-off-by: default avatarChristoffer Dall <christoffer.dall@linaro.org>
parent 2cccbb36

virt/kvm/arm/vgic/vgic-mmio-v3.c

+16 −10
Original line number Diff line number Diff line
@@ -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;



	do {

		old_propbaser = dist->propbaser;

		propbaser = old_propbaser;

		propbaser = update_64bit_reg(propbaser, addr & 4, len, val);

		propbaser = vgic_sanitise_propbaser(propbaser);



	dist->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;



	do {

		old_pendbaser = vgic_cpu->pendbaser;

		pendbaser = old_pendbaser;

		pendbaser = update_64bit_reg(pendbaser, addr & 4, len, val);

		pendbaser = vgic_sanitise_pendbaser(pendbaser);



	vgic_cpu->pendbaser = pendbaser;

	} while (cmpxchg64(&vgic_cpu->pendbaser, old_pendbaser,

			   pendbaser) != old_pendbaser);

}



/*