KVM: x86: Bail to userspace if emulation of atomic user access faults

Exit to userspace when emulating an atomic guest access if the CMPXCHG on
the userspace address faults.  Emulating the access as a write and thus
likely treating it as emulated MMIO is wrong, as KVM has already
confirmed there is a valid, writable memslot.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220202004945.2540433-6-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index e5b0dd24b200aa5a62b4265c77a1c841476b7bad..4e7f3a8da16a65d3cf1d457380f1343a2ceba77f 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7319,7 +7319,7 @@ static int emulator_cmpxchg_emulated(struct x86_emulate_ctxt *ctxt,
        }
 
        if (r < 0)
-               goto emul_write;
+               return X86EMUL_UNHANDLEABLE;
        if (r)
                return X86EMUL_CMPXCHG_FAILED;