_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.
This became necessary because Xen started checking for this bit, rather
than silently masking it off.
Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
---
arch/x86/xen/mmu.c | 4 ++++
1 file changed, 4 insertions(+)
===================================================================
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -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 };
}
-
