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Date:	Tue, 16 Jun 2015 10:19:43 -0400
From:	Boris Ostrovsky <>
To:	David Vrabel <>,
	Ingo Molnar <>
CC:	Ian Campbell <>,
	Konrad Rzeszutek Wilk <>,,,,
	Andy Lutomirski <>,
	Andrew Morton <>,
	Denys Vlasenko <>,
	Brian Gerst <>,
	Peter Zijlstra <>,
	Borislav Petkov <>,
	"H. Peter Anvin" <>,
	Linus Torvalds <>,
	Oleg Nesterov <>,
	Thomas Gleixner <>,
	Waiman Long <>
Subject: Re: [PATCH 07/12] x86/virt/guest/xen: Remove use of pgd_list from
 the Xen guest code

On 06/16/2015 10:15 AM, David Vrabel wrote:
> On 15/06/15 21:35, Ingo Molnar wrote:
>> * David Vrabel <> 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.


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