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Date:	Tue, 16 Jun 2015 15:15:48 +0100
From:	David Vrabel <>
To:	Ingo Molnar <>
CC:	Ian Campbell <>,
	Konrad Rzeszutek Wilk <>,
	Boris Ostrovsky <>,
	<>, <>,
	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 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.

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