x86/vMSI-X: write snoops should ignore hvm_mmio_internal() requests

Those aren't actual I/O requests (and hence are of no interest here
anyway). Since they don't get copied into struct vcpu, looking at that
copy reads whatever was left there. Use the state of the request to
determine its validity.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/hvm/vmsi.c
+++ b/xen/arch/x86/hvm/vmsi.c
@@ -349,6 +349,8 @@ static int msixtbl_range(struct vcpu *v,
     {
         const ioreq_t *r = &v->arch.hvm_vcpu.hvm_io.io_req;
 
+        if ( r->state != STATE_IOREQ_READY )
+            return 0;
         ASSERT(r->type == IOREQ_TYPE_COPY);
         if ( r->dir == IOREQ_WRITE && r->size == 4 && !r->data_is_ptr
              && !(r->data & PCI_MSIX_VECTOR_BITMASK) )