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ARM: 7985/1: mm: implement pte_accessible for faulting mappings

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The pte_accessible macro can be used to identify page table entries
capable of being cached by a TLB. In principle, this differs from
pte_present, since PROT_NONE mappings are mapped using invalid entries
identified as present and ptes designated as `old' can use either
invalid entries or those with the access flag cleared (guaranteed not to
be in the TLB). However, there is a race to take care of, as described
in 2084140594 ("mm: fix TLB flush race between migration, and
change_protection_range"), between a page being migrated and mprotected
at the same time. In this case, we can check whether a TLB invalidation
is pending for the mm and if so, temporarily consider PROT_NONE mappings
as valid.

This patch implements a quick pte_accessible macro for ARM by simply
checking if the pte is valid/present depending on the mm. For classic
MMU, these checks are identical and will generate some false positives
for PROT_NONE mappings, but this is better than the current asm-generic
definition of ((void)(pte),1).

Finally, pte_present_user is moved to use pte_valid (and renamed
appropriately) since we don't care about cache flushing for faulting
mappings.

Acked-by: Steve Capper <steve.capper@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
This commit is contained in:
Will Deacon 2014-02-21 17:01:48 +01:00 committed by Russell King
parent c32ffce0f6
commit 1971188aa1
1 changed files with 5 additions and 2 deletions
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7
arch/arm/include/asm/pgtable.h
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@ -216,13 +216,16 @@ static inline pte_t *pmd_page_vaddr(pmd_t pmd)
#define pte_none(pte) (!pte_val(pte))
#define pte_present(pte) (pte_val(pte) & L_PTE_PRESENT)
#define pte_valid(pte) (pte_val(pte) & L_PTE_VALID)
#define pte_accessible(mm, pte) (mm_tlb_flush_pending(mm) ? pte_present(pte) : pte_valid(pte))
#define pte_write(pte) (!(pte_val(pte) & L_PTE_RDONLY))
#define pte_dirty(pte) (pte_val(pte) & L_PTE_DIRTY)
#define pte_young(pte) (pte_val(pte) & L_PTE_YOUNG)
#define pte_exec(pte) (!(pte_val(pte) & L_PTE_XN))
#define pte_special(pte) (0)
#define pte_present_user(pte) (pte_present(pte) && (pte_val(pte) & L_PTE_USER))
#define pte_valid_user(pte) \
(pte_valid(pte) && (pte_val(pte) & L_PTE_USER) && pte_young(pte))
#if __LINUX_ARM_ARCH__ < 6
static inline void __sync_icache_dcache(pte_t pteval)
@ -237,7 +240,7 @@ static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
{
unsigned long ext = 0;
if (addr < TASK_SIZE && pte_present_user(pteval)) {
if (addr < TASK_SIZE && pte_valid_user(pteval)) {
__sync_icache_dcache(pteval);
ext |= PTE_EXT_NG;
}