linux-kernel - Re: [PATCHv2 1/3] x86/mm: Provide pmdp

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Date:   Wed, 21 Jun 2017 20:52:03 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Vineet Gupta <Vineet.Gupta1@...opsys.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Russell King <linux@...linux.org.uk>,
        Will Deacon <will.deacon@....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>,
        Andrea Arcangeli <aarcange@...hat.com>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCHv2 1/3] x86/mm: Provide pmdp_establish() helper

On Wed, Jun 21, 2017 at 10:20:47AM -0700, Vineet Gupta wrote:
> On 06/21/2017 10:16 AM, Kirill A. Shutemov wrote:
> > On Wed, Jun 21, 2017 at 08:49:03AM -0700, Vineet Gupta wrote:
> > > On 06/21/2017 04:27 AM, Catalin Marinas wrote:
> > > > On Wed, Jun 21, 2017 at 12:53:03PM +0300, Kirill A. Shutemov wrote:
> > > > > > > > > > On Thu, Jun 15, 2017 at 05:52:22PM +0300, Kirill A. Shutemov wrote:
> > > > > > > > > > > We need an atomic way to setup pmd page table entry, avoiding races with
> > > > > > > > > > > CPU setting dirty/accessed bits. This is required to implement
> > > > > > > > > > > pmdp_invalidate() that doesn't loose these bits.
> > > > [...]
> > > > > Any chance you could help me with arm too?
> > > > On arm (ARMv7 with LPAE) we don't have hardware updates of the
> > > > access/dirty bits, so a generic implementation would suffice. I didn't
> > > > find one in your patches, so here's an untested version:
> > > > 
> > > > static inline pmd_t pmdp_establish(struct mm_struct *mm, unsigned long address,
> > > > 				   pmd_t *pmdp, pmd_t pmd)
> > > > {
> > > > 	pmd_t old_pmd = *pmdp;
> > > > 	set_pmd_at(mm, address, pmdp, pmd);
> > > > 	return old_pmd;
> > > > }
> > > So it seems the discussions have settled down and pmdp_establish() can be
> > > implemented in generic way as above and it will suffice if arch doesn't have
> > > a special need. It would be nice to add the comment above generic version
> > > that it only needs to be implemented if hardware sets the accessed/dirty
> > > bits !
> > > 
> > > Then nothing special is needed for ARC - right ?
> > I will define generic version as Catalin proposed with a comment, but
> > under the name generic_pmdp_establish. An arch can make use of it by
> > 
> > #define pmdp_establish generic_pmdp_establish
> 
> Can you do that for ARC in your next posting - or want me to once you have
> posted that ?

I'll do this.

-- 
 Kirill A. Shutemov