From 593befa6ab74a805e4f503c8c737c3cffa8066b6 Mon Sep 17 00:00:00 2001 From: Dominik Dingel Date: Thu, 23 Oct 2014 12:07:44 +0200 Subject: [PATCH] mm: introduce mm_forbids_zeropage function Add a new function stub to allow architectures to disable for an mm_structthe backing of non-present, anonymous pages with read-only empty zero pages. Signed-off-by: Dominik Dingel Reviewed-by: Paolo Bonzini Signed-off-by: Martin Schwidefsky --- include/linux/mm.h | 11 +++++++++++ mm/huge_memory.c | 2 +- mm/memory.c | 2 +- 3 files changed, 13 insertions(+), 2 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index 27eb1bfbe704..ab7dadca4ea5 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -56,6 +56,17 @@ extern int sysctl_legacy_va_layout; #define __pa_symbol(x) __pa(RELOC_HIDE((unsigned long)(x), 0)) #endif +/* + * To prevent common memory management code establishing + * a zero page mapping on a read fault. + * This macro should be defined within . + * s390 does this to prevent multiplexing of hardware bits + * related to the physical page in case of virtualization. + */ +#ifndef mm_forbids_zeropage +#define mm_forbids_zeropage(X) (0) +#endif + extern unsigned long sysctl_user_reserve_kbytes; extern unsigned long sysctl_admin_reserve_kbytes; diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 74c78aa8bc2f..7e9c15cb93a9 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -805,7 +805,7 @@ int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma, return VM_FAULT_OOM; if (unlikely(khugepaged_enter(vma))) return VM_FAULT_OOM; - if (!(flags & FAULT_FLAG_WRITE) && + if (!(flags & FAULT_FLAG_WRITE) && !mm_forbids_zeropage(mm) && transparent_hugepage_use_zero_page()) { spinlock_t *ptl; pgtable_t pgtable; diff --git a/mm/memory.c b/mm/memory.c index 1cc6bfbd872e..d722d4f481c9 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -2640,7 +2640,7 @@ static int do_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma, return VM_FAULT_SIGBUS; /* Use the zero-page for reads */ - if (!(flags & FAULT_FLAG_WRITE)) { + if (!(flags & FAULT_FLAG_WRITE) && !mm_forbids_zeropage(mm)) { entry = pte_mkspecial(pfn_pte(my_zero_pfn(address), vma->vm_page_prot)); page_table = pte_offset_map_lock(mm, pmd, address, &ptl); -- 2.20.1