From: Jeremy Fitzhardinge _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 Signed-off-by: Andrew Morton --- arch/x86/xen/mmu.c | 4 ++++ 1 file changed, 4 insertions(+) diff -puN arch/x86/xen/mmu.c~xen-mask-_page_pcd-from-ptes arch/x86/xen/mmu.c --- a/arch/x86/xen/mmu.c~xen-mask-_page_pcd-from-ptes +++ a/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 }; } @@ -291,6 +293,8 @@ 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 }; } _