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

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Message-ID: <20170621112702.GC10220@e104818-lin.cambridge.arm.com>
Date:   Wed, 21 Jun 2017 12:27:02 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
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>,
        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-mm@...ck.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 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;
}

-- 
Catalin