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SubjectRe: [PATCHv2 2/3] mm: Do not loose dirty and access bits in pmdp_invalidate()
On Fri, Jun 16, 2017 at 03:40:41PM +0200, Andrea Arcangeli wrote:
> On Thu, Jun 15, 2017 at 05:52:23PM +0300, Kirill A. Shutemov wrote:
> > -void pmdp_invalidate(struct vm_area_struct *vma, unsigned long address,
> > +pmd_t pmdp_invalidate(struct vm_area_struct *vma, unsigned long address,
> > pmd_t *pmdp)
> > {
> > - pmd_t entry = *pmdp;
> > - set_pmd_at(vma->vm_mm, address, pmdp, pmd_mknotpresent(entry));
> > - flush_pmd_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
> > + pmd_t old = pmdp_establish(pmdp, pmd_mknotpresent(*pmdp));
> > + if (pmd_present(old))
> > + flush_pmd_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
> > + return old;
> > }
> > #endif
>
> The pmd_present() check added above is superflous because there's no
> point to call pmdp_invalidate if the pmd is not present (present as in
> pmd_present) already. pmd_present returns true if _PAGE_PSE is set
> and it was always set before calling pmdp_invalidate.
>
> It looks like we could skip the flush if _PAGE_PRESENT is not set
> (i.e. for example if the pmd is PROTNONE) but that's not what the above
> pmd_present will do.

You are right. We seems don't have a generic way to check the entry is
present to CPU.

I guess I'll drop the check then.

--
Kirill A. Shutemov

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