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mm: introduce mm_forbids_zeropage function

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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 <dingel@linux.vnet.ibm.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Dominik Dingel 2014-10-23 12:07:44 +02:00 committed by Martin Schwidefsky
parent a13cff318c
commit 593befa6ab
3 changed files with 13 additions and 2 deletions
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11
include/linux/mm.h
View file

@ -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 <asm/pgtable.h>.
* 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;

2
mm/huge_memory.c
View file

@ -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;

2
mm/memory.c
View file

@ -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);