x86/shadow: add a clarifying assertion

... documenting that we don't have to worry about merging guest
provided flags with the ones we want to enforce ourselves.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Tim Deegan <tim@xen.org>

diff --git a/xen/arch/x86/mm/shadow/multi.c b/xen/arch/x86/mm/shadow/multi.c
index 5c7a7ace6bf5795c8f94b286274e6b3ed2f1b5fd..3c1b25b998ba9b7bafcec74a198cfba4e1f14cdd 100644 (file)
--- a/xen/arch/x86/mm/shadow/multi.c
+++ b/xen/arch/x86/mm/shadow/multi.c
@@ -592,6 +592,8 @@ _sh_propagate(struct vcpu *v,
     {
         unsigned int type;
 
+        ASSERT(!(sflags & (_PAGE_PAT | _PAGE_PCD | _PAGE_PWT)));
+
         /* compute the PAT index for shadow page entry when VT-d is enabled
          * and device assigned. 
          * 1) direct MMIO: compute the PAT index with gMTRR=UC and gPAT.