xen: mask _PAGE_PCD from ptes

_PAGE_PCD maps a page with caching disabled, which is typically used for mapping harware registers. Xen never allows it to be set on a mapping, and unprivileged guests never need it since they can't see the real underlying hardware. However, some uncached mappings are made early when probing the (non-existent) APIC, and its OK to mask off the PCD flag in these cases.

---
 arch/x86/xen/mmu.c |    4 ++++
 1 file changed, 4 insertions(+)

===================================================================

@@ -244,6 +244,8 @@ pte_t xen_make_pte(unsigned long long pt
 	if (pte & 1)
 		pte = phys_to_machine(XPADDR(pte)).maddr;
 
+	pte &= ~_PAGE_PCD;
+
 	return (pte_t){ pte, pte >> 32 };
 }
 

@@ -290,6 +292,8 @@ pte_t xen_make_pte(unsigned long pte)
 {
 	if (pte & _PAGE_PRESENT)
 		pte = phys_to_machine(XPADDR(pte)).maddr;
+
+	pte &= ~_PAGE_PCD;
 
 	return (pte_t){ pte };
 }