From 66a27dde9ae96e35278983f2e59bea04eb714cd0 Mon Sep 17 00:00:00 2001 From: David Vrabel Date: Mon, 9 Jul 2012 11:39:06 +0100 Subject: [PATCH] xen/mm: zero PTEs for non-present MFNs in the initial page table 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 Signed-off-by: Konrad Rzeszutek Wilk --- arch/x86/xen/mmu.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c index 3f1783a79a3c..27336dfcda8e 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); } -- 2.39.5