Re: [PATCH 07/12] x86/virt/guest/xen: Remove use of pgd_list from the Xen guest code

[David Vrabel]

On 15/06/15 21:35, Ingo Molnar wrote:
> 
> * David Vrabel <david.vrabel@xxxxxxxxxx> 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.

David
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