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Subject[PATCH 1/2] xen: mask unwanted pte bits in __supported_pte_mask
Rather than ad-hoc masking unwanted bits when constructing a pte, just
prevent them from ever being set by removing them from
__supported_pte_mask.

[ Stable: this isn't a bugfix in itself, but it's a pre-requiste
for "xen: don't drop NX bit" ]

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc: Stable Kernel <stable@kernel.org>
---
arch/x86/xen/enlighten.c | 5 +++++
arch/x86/xen/mmu.c | 4 +---
2 files changed, 6 insertions(+), 3 deletions(-)

===================================================================
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1294,6 +1294,11 @@
if (xen_feature(XENFEAT_supervisor_mode_kernel))
pv_info.kernel_rpl = 0;

+ /* Prevent unwanted bits from being set in PTEs. */
+ __supported_pte_mask &= ~_PAGE_GLOBAL;
+ if (!is_initial_xendomain())
+ __supported_pte_mask &= ~(_PAGE_PWT | _PAGE_PCD);
+
/* set the limit of our address space */
xen_reserve_top();

===================================================================
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -375,10 +375,8 @@

pte_t xen_make_pte(pteval_t pte)
{
- if (pte & _PAGE_PRESENT) {
+ if (pte & _PAGE_PRESENT)
pte = phys_to_machine(XPADDR(pte)).maddr;
- pte &= ~(_PAGE_PCD | _PAGE_PWT);
- }

return (pte_t){ .pte = pte };
}


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