KVM: arm64: Fix read-side race on updates to vcpu reset state

KVM: arm64: Fix read-side race on updates to vcpu reset state

[ Upstream commit 6654f9dfcb88fea3b9affc180dc3c04333d0f306 ]

KVM correctly serializes writes to a vCPU's reset state, however since
we do not take the KVM lock on the read side it is entirely possible to
read state from two different reset requests.

Cure the race for now by taking the KVM lock when reading the
reset_state structure.

Fixes: 358b28f09f0a ("arm/arm64: KVM: Allow a VCPU to fully reset itself")
Signed-off-by: Oliver Upton <oupton@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210818202133.1106786-2-oupton@google.com
Signed-off-by: Sasha Levin <sashal@kernel.org>