linux-kernel - Re: [PATCH v2 2/2] x86/mm: implement free pmd/pte page interfaces

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Message-ID: <fb4771ca-694b-8a52-d239-1c730617600b@codeaurora.org>
Date:   Fri, 27 Apr 2018 19:12:57 +0530
From:   Chintan Pandya <cpandya@...eaurora.org>
To:     "joro@...tes.org" <joro@...tes.org>
Cc:     "guohanjun@...wei.com" <guohanjun@...wei.com>,
        "Hocko, Michal" <MHocko@...e.com>,
        "Kani, Toshi" <toshi.kani@....com>,
        "wxf.wang@...ilicon.com" <wxf.wang@...ilicon.com>,
        "catalin.marinas@....com" <catalin.marinas@....com>,
        "x86@...nel.org" <x86@...nel.org>,
        "will.deacon@....com" <will.deacon@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "willy@...radead.org" <willy@...radead.org>,
        "hpa@...or.com" <hpa@...or.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "bp@...e.de" <bp@...e.de>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 2/2] x86/mm: implement free pmd/pte page interfaces

On 4/27/2018 6:18 PM, joro@...tes.org wrote:
> On Fri, Apr 27, 2018 at 05:22:28PM +0530, Chintan Pandya wrote:
>> I'm bit confused here. Are you pointing to race within ioremap/vmalloc
>> framework while updating the page table or race during tlb ops. Since
>> later is arch dependent, I would not comment. But if the race being
>> discussed here while altering page tables, I'm not on the same page.
> 
> The race condition is between hardware and software. It is not
> sufficient to just remove the software references to the page that is
> about to be freed (by clearing the PMD/PUD), also the hardware
> references in the page-walk cache need to be removed with a TLB flush.
> Otherwise the hardware can use the freed (and possibly reused) page to
> establish new TLB entries.

Sure ! This is my understanding too (from arm64 context).

> 
> 
> 
> 	Joerg
> 
> 
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> 

Chintan
-- 
Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center,
Inc. is a member of the Code Aurora Forum, a Linux Foundation
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