linux-kernel - Re: [PATCHv2 2/3] mm: Do not loose dirty and access bits in pmdp

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Message-ID: <20170619132913.se67bp4addreqovn@node.shutemov.name>
Date:   Mon, 19 Jun 2017 16:29:13 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Andrea Arcangeli <aarcange@...hat.com>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Vineet Gupta <vgupta@...opsys.com>,
        Russell King <linux@...linux.org.uk>,
        Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Ralf Baechle <ralf@...ux-mips.org>,
        "David S. Miller" <davem@...emloft.net>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        linux-arch@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [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