Hi Will,
On Mon, Oct 01, 2012 at 02:51:45PM +0100, Will Deacon wrote:
> +void huge_pmd_set_accessed(struct mm_struct *mm, struct vm_area_struct *vma,
> + unsigned long address, pmd_t *pmd, pmd_t orig_pmd)
> +{
> + pmd_t entry;
> +
> + spin_lock(&mm->page_table_lock);
> + entry = pmd_mkyoung(orig_pmd);
> + if (pmdp_set_access_flags(vma, address & HPAGE_PMD_MASK, pmd, entry, 0))
> + update_mmu_cache(vma, address, pmd);
If the pmd is being splitted, this may not be a trasnhuge pmd anymore
by the time you obtained the lock. (orig_pmd could be stale, and it
wasn't verified with pmd_same either)
The lock should be obtained through pmd_trans_huge_lock.
if (pmd_trans_huge_lock(orig_pmd, vma) == 1)
{
set young bit
spin_unlock(&mm->page_table_lock);
}
On x86:
int pmdp_set_access_flags(struct vm_area_struct *vma,
unsigned long address, pmd_t *pmdp,
pmd_t entry, int dirty)
{
int changed = !pmd_same(*pmdp, entry);
VM_BUG_ON(address & ~HPAGE_PMD_MASK);
if (changed && dirty) {
*pmdp = entry;
with dirty == 0 it looks like it won't make any difference, but I
guess your arm pmdp_set_access_flag is different.
However it seems "dirty" means write access and so the invocation
would better match the pte case:
if (pmdp_set_access_flags(vma, address & HPAGE_PMD_MASK, pmd, entry,
flags & FAULT_FLAG_WRITE))
But note, you still have to update it even when "dirty" == 0, or it'll
still infinite loop for read accesses.
> + spin_unlock(&mm->page_table_lock);
> +}
> +
> int do_huge_pmd_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
> unsigned long address, pmd_t *pmd, pmd_t orig_pmd)
> {
> diff --git a/mm/memory.c b/mm/memory.c
> index 5736170..d5c007d 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3537,7 +3537,11 @@ retry:
> if (unlikely(ret & VM_FAULT_OOM))
> goto retry;
> return ret;
> + } else {
> + huge_pmd_set_accessed(mm, vma, address, pmd,
> + orig_pmd);
> }
> +
> return 0;
Thanks,
Andrea
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