Re: [PATCHv2 2/3] mm: Do not loose dirty and access bits in pmdp_invalidate()

[Kirill A. Shutemov]

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