linux-kernel - Re: [PATCH] mm: Fix potential pte_unmap

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Date:   Fri, 22 Jan 2021 16:27:23 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
CC:     <tglx@...utronix.de>, <dave.hansen@...el.com>,
        <jpoimboe@...hat.com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>, Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH] mm: Fix potential pte_unmap_unlock pte error

Hi Andrew:
On 2021/1/14 10:51, Miaohe Lin wrote:
> Hi:
> On 2021/1/11 1:14, Andi Kleen wrote:
>> On Sat, Jan 09, 2021 at 03:01:18AM -0500, Miaohe Lin wrote:
>>> Since commit 42e4089c7890 ("x86/speculation/l1tf: Disallow non privileged
>>> high MMIO PROT_NONE mappings"), when the first pfn modify is not allowed,
>>> we would break the loop with pte unchanged. Then the wrong pte - 1 would
>>> be passed to pte_unmap_unlock.
>>
>> Thanks.
>>
>> While the fix is correct, I'm not sure if it actually is a real bug. Is there
>> any architecture that would do something else than unlocking the underlying
>> page?  If it's just the underlying page then it should be always the same
>> page, so no bug.
>>
> 
> It's just a theoretical issue via code inspection.

Should I send a new one without Cc statle or just drop this patch? Thanks.

> 
>> That said of course the change is the right thing for main line, but probably doesn't
>> need to be backported.
>>
> 
> So it should not be backported. Should I resend a patch or Andrew would kindly do this?
> 
>> -Andi
>> .
>>
> 
> Many thanks for review and reply.
>