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Date: Tue, 16 Jun 2015 15:27:57 +0100
From: David Vrabel <david.vrabel@citrix.com>
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To: Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Ingo Molnar <mingo@kernel.org>
CC: Ian Campbell <ijc@hellion.org.uk>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        <linux-kernel@vger.kernel.org>, <linux-mm@kvack.org>,
        <xen-devel@lists.xenproject.org>,
        Andy Lutomirski <luto@amacapital.net>,
        Andrew Morton <akpm@linux-foundation.org>,
        "Denys Vlasenko" <dvlasenk@redhat.com>,
        Brian Gerst <brgerst@gmail.com>,
        "Peter Zijlstra" <peterz@infradead.org>,
        Borislav Petkov <bp@alien8.de>, "H. Peter Anvin" <hpa@zytor.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        "Oleg Nesterov" <oleg@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>, Waiman Long <Waiman.Long@hp.com>
Subject: Re: [PATCH 07/12] x86/virt/guest/xen: Remove use of pgd_list from
 the Xen guest code
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On 16/06/15 15:19, Boris Ostrovsky wrote:
> On 06/16/2015 10:15 AM, David Vrabel wrote:
>> On 15/06/15 21:35, Ingo Molnar wrote:
>>> * David Vrabel <david.vrabel@citrix.com> wrote:
>>>
>>>> On 15/06/15 10:05, Ian Campbell wrote:
>>>>> On Sat, 2015-06-13 at 11:49 +0200, Ingo Molnar wrote:
>>>>>> xen_mm_pin_all()/unpin_all() are used to implement full guest
>>>>>> instance
>>>>>> suspend/restore. It's a stop-all method that needs to iterate
>>>>>> through all
>>>>>> allocated pgds in the system to fix them up for Xen's use.
>>>>>>
>>>>>> This code uses pgd_list, probably because it was an easy interface.
>>>>>>
>>>>>> But we want to remove the pgd_list, so convert the code over to
>>>>>> walk all
>>>>>> tasks in the system. This is an equivalent method.
>>>> It is not equivalent because pgd_alloc() now populates entries in
>>>> pgds that are
>>>> not visible to xen_mm_pin_all() (note how the original code adds the
>>>> pgd to the
>>>> pgd_list in pgd_ctor() before calling pgd_prepopulate_pmd()).  These
>>>> newly
>>>> allocated page tables won't be correctly converted on suspend/resume
>>>> and the new
>>>> process will die after resume.
>>> So how should the Xen logic be fixed for the new scheme? I can't say
>>> I can see
>>> through the paravirt complexity here.
>> Actually, since we freeze_processes() before trying to pin page tables,
>> I think it should be ok as-is.
>>
>> I'll put the patch through some tests.
> 
> Actually, I just ran this through a couple of boot/suspend/resume tests
> and didn't see any issues (with the one fix I mentioned to Ingo
> earlier). On unstable Xen only.

In which case this can have a:

Reviewed-by: David Vrabel <david.vrabel@citrix.com>

Thanks.

David