[PATCH] KVM: arm64: nv: Initialize hw_mmu to NULL for nested vCPUs

[Dan Carpenter <dan@cryspen.com>]

Before commit 6ded46b5a4fd ("KVM: arm64: nv: Keep reference on stage-2
MMU when scheduled out"), kvm_vcpu_load_hw_mmu() would set ->hw_mmu on
every load.  Now it only sets it when it is set to NULL.

In kvm_vcpu_init_nested() the vcpu->arch.hw_mmu points to &kvm->arch.mmu
from when it was set in kvm_arch_vcpu_create().

Normally what happens next is a two step process.  KVM_ARM_VCPU_INIT
calls kvm_reset_vcpu_core() and that sets the vcpu into hyp context
(vEL2).  Then KVM_RUN calls kvm_vcpu_load_hw_mmu() which doesn't do
anything.  But that is fine because we are in hyp context and the
->hw_mmu already is pointing to the correct place.

However if, for example, we are restoring a vcpu that was saved in L2
context, then the VMM uses KVM_SET_ONE_REG to overwrite the vEL2 state
that kvm_reset_vcpu_core() set up, and the vCPU is in L2 context when
KVM_RUN loads it for the first time.  Ideally, kvm_vcpu_load_hw_mmu()
would set the hw_mm to point to L2's page tables but, since is non-NULL,
it leaves it as is.  At this point L2 can access L1's memory.

Fix this bug but setting ->hw_mmu to NULL in kvm_vcpu_init_nested() so
that kvm_vcpu_load_hw_mmu() always sets it correctly on the first load.

Fixes: 6ded46b5a4fd ("KVM: arm64: nv: Keep reference on stage-2 MMU when scheduled out")
Cc: stable@vger.kernel.org
Signed-off-by: Dan Carpenter <dan@cryspen.com>
---
 arch/arm64/kvm/nested.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c
index 78fa433774c6..60bccb66e52c 100644
--- a/arch/arm64/kvm/nested.c
+++ b/arch/arm64/kvm/nested.c
@@ -140,6 +140,8 @@ int kvm_vcpu_init_nested(struct kvm_vcpu *vcpu)
 		kvm->arch.nested_mmus_size += S2_MMU_PER_VCPU;
 	}
 
+	vcpu->arch.hw_mmu = NULL;
+
 	return 0;
 }
 
-- 
2.53.0