From: David Vrabel <david.vra...@citrix.com>
When constructing the initial page tables, if the MFN for a usable PFN
is missing in the p2m then that frame is initially ballooned out. In
this case, zero the PTE (as in decrease_reservation() in
drivers/xen/balloon.c).
This is obviously safe instead of having an valid PTE with an MFN of
INVALID_P2M_ENTRY (~0).
Signed-off-by: David Vrabel <david.vra...@citrix.com>
---
arch/x86/xen/mmu.c | 9 ++++++++-
1 files changed, 8 insertions(+), 1 deletions(-)
diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index 3f1783a..27336df 100644
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -1432,6 +1432,10 @@ static pte_t __init mask_rw_pte(pte_t *ptep, pte_t pte)
* Init-time set_pte while constructing initial pagetables, which
* doesn't allow RO page table pages to be remapped RW.
*
+ * If there is no MFN for this PFN then this page is initially
+ * ballooned out so clear the PTE (as in decrease_reservation() in
+ * drivers/xen/balloon.c).
+ *
* Many of these PTE updates are done on unpinned and writable pages
* and doing a hypercall for these is unnecessary and expensive. At
* this point it is not possible to tell if a page is pinned or not,
@@ -1440,7 +1444,10 @@ static pte_t __init mask_rw_pte(pte_t *ptep, pte_t pte)
*/
static void __init xen_set_pte_init(pte_t *ptep, pte_t pte)
{
- pte = mask_rw_pte(ptep, pte);
+ if (pte_mfn(pte) != INVALID_P2M_ENTRY)
+ pte = mask_rw_pte(ptep, pte);
+ else
+ pte = __pte_ma(0);
native_set_pte(ptep, pte);
}
--
1.7.2.5
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