[PATCH 1/4] KVM: x86/mmu: Return -EIO if page fault returns RET_PF_INVALID

[Sean Christopherson <sean.j.christopherson@intel.com>]

Exit to userspace with an error if the MMU is buggy and returns
RET_PF_INVALID when servicing a page fault.  This will allow a future
patch to invert the emulation path, i.e. emulate only on RET_PF_EMULATE
instead of emulating on anything but RET_PF_RETRY.  This technically
means that KVM will exit to userspace instead of emulating on
RET_PF_INVALID, but practically speaking it's a nop as the MMU never
returns RET_PF_INVALID.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
 arch/x86/kvm/mmu/mmu.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 76c5826e29a2..4a2a8f67a8f7 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -5450,7 +5450,8 @@ int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, u64 error_code,
 	if (r == RET_PF_INVALID) {
 		r = kvm_mmu_do_page_fault(vcpu, cr2_or_gpa,
 					  lower_32_bits(error_code), false);
-		WARN_ON(r == RET_PF_INVALID);
+		if (WARN_ON_ONCE(r == RET_PF_INVALID))
+			return -EIO;
 	}
 
 	if (r == RET_PF_RETRY)
-- 
2.28.0