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

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 06/16/2015 10:15 AM, David Vrabel wrote:
> 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.
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.
-boris



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