Date: Wed, 21 Jun 2017 20:15:58 +0300
From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Vineet Gupta <Vineet.Gupta1@synopsys.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Vlastimil Babka <vbabka@suse.cz>, Russell King <linux@armlinux.org.uk>,
        Will Deacon <will.deacon@arm.com>, Ralf Baechle <ralf@linux-mips.org>,
        "David S. Miller" <davem@davemloft.net>,
        "Aneesh Kumar K . V" <aneesh.kumar@linux.vnet.ibm.com>,
        Martin Schwidefsky <schwidefsky@de.ibm.com>,
        Heiko Carstens <heiko.carstens@de.ibm.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@kernel.org>, "H . Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCHv2 1/3] x86/mm: Provide pmdp_establish() helper
Message-ID: <20170621171558.7zrgzc7uk3kspcys@node.shutemov.name>
References: <20170615145224.66200-1-kirill.shutemov@linux.intel.com>
 <20170615145224.66200-2-kirill.shutemov@linux.intel.com>
 <20170619152228.GE3024@e104818-lin.cambridge.arm.com>
 <20170619160005.wgj4nymtj2nntfll@node.shutemov.name>
 <20170619170911.GF3024@e104818-lin.cambridge.arm.com>
 <20170619215210.2crwjou3sfdcj73d@node.shutemov.name>
 <20170620155438.GC21383@e104818-lin.cambridge.arm.com>
 <20170621095303.q5fqt5a3ao5smko6@node.shutemov.name>
 <20170621112702.GC10220@e104818-lin.cambridge.arm.com>
 <1af1738a-88a7-987c-eca7-2118d66514e1@synopsys.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <1af1738a-88a7-987c-eca7-2118d66514e1@synopsys.com>
User-Agent: NeoMutt/20170609 (1.8.3)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1729
Lines: 40

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

I don't want it to be used by default without attention from architecture
maintainer. It can lead unnoticied breakage if THP got enabled on new
arch.

-- 
 Kirill A. Shutemov