linux-kernel - Re: [PATCH] x86: fix {pmd,pud}_{set,clear}

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Date:   Mon, 19 Feb 2018 18:41:22 +0100
From:   Juergen Gross <jgross@...e.com>
To:     Jan Beulich <JBeulich@...e.com>
Cc:     Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        lkml <linux-kernel@...r.kernel.org>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] x86: fix {pmd,pud}_{set,clear}_flags()

On 19/02/18 18:04, Jan Beulich wrote:
>>>> On 19.02.18 at 17:23, <jgross@...e.com> wrote:
>> On 19/02/18 15:48, Jan Beulich wrote:
>>> Just like pte_{set,clear}_flags() their PMD and PUD counterparts should
>>> not do any address translation. This was outright wrong under Xen
>>> (causing a dead boot with no useful output on "suitable" systems), and
>>> produced needlessly more complicated code (even if just slightly) when
>>> paravirt was enabled.
>>>
>>> Signed-off-by: Jan Beulich <jbeulich@...e.com>
>>> Cc: stable@...r.kernel.org 
>>
>> While the changes look alright I'm really curious which kind of failure
>> you are seeing, especially considering how long those functions haven't
>> been changed (since more than 6 years).
> 
> It's the new use of pmd_set_flags() in 2cc42bac1c ("x86-64/Xen:
> eliminate W+X mappings"), and due to the (very odd afaic) identity
> map handling the issue is invisible on most systems/setups.

Aah, okay. This helps.

Reviewed-by: Juergen Gross <jgross@...e.com>


Juergen