Re: [Xen-devel] questions of vm save/restore on arm64

[Chenxiao Zhao <chenxiao.zhao@xxxxxxxxx>]

On 6/3/2016 4:02 AM, Julien Grall wrote:
> Hello,
>
> First thing, the time in the mail headers seems to be wrong. Maybe
> because of a wrong timezone?
>
> I got: 04/06/16 02:32 however we are still the 3rd in my timezone.
>
> On 04/06/16 02:32, Chenxiao Zhao wrote:
> > On 6/3/2016 3:16 AM, Julien Grall wrote:
> > > Hello,
> > >
> > > On 03/06/16 18:05, Chenxiao Zhao wrote:
> > > > I finally found out that the problem is that the toolstack did not get
> > > > corret p2m_size while sending all pages on save(always be zero).
> > > > After I
> > > > fixed that, the guest could be restored but guest kernel caught
> > > > handle_mm_fault().
> > > >
> > > > where do you think I'm going to investigate, guest kernel hibernation
> > > > restore or xen?
> > > The hibernation support for ARM64 has only been merged recently in the
> > > kernel. Which kernel are you using?
> > Hi Julien,
> >
> > I'm using a linaro ported Linux kernel 4.1 for hikey from this link.
> >
> > https://github.com/96boards/linux/tree/android-hikey-linaro-4.1
> >
> > I also applied following patches to make the kernel support hibernation.
> This looks the wrong way to do it as this series may requires some
> patches which have been upstreamed before hand.
>
> Linux upstream seems support to the hikey board [1]. Any reason to not
> using it?
I tried a newer version of kernel 4.4, but got no luck to start dom0 
with xen. so I decide to stay in 4.1 for now.
> > [1] http://www.spinics.net/lists/arm-kernel/msg477769.html
> > [2] http://lists.xen.org/archives/html/xen-devel/2015-12/msg01068.html
> >
> > > Also, what are the modifications you have made to support Xen
> > > suspend/resume for ARM64?
> > I believe I have posted my modifications on xen in the first mail of
> > this thread.
> I mean in Linux. The patch from Ian Campbell does not have any kind of
> support for ARM64.
>
> For instance arch/arm/xen/suspend.c needs to be built for ARM64. So I am
> wondering if your kernel has support of hibernation...
Oh, yes, I most forgot I added this file in arch/arm64/xen/Makefile to 
let it build for arm64.
> >  From my understanding, a kernel hibernation will cause kernel to save
> > memories to disk(swap partition). But on guest save progress, the
> > hibernation for domU does not make the guest save memories to disk. it's
> > more like suspend all processes in guest, and memors actually depends on
> > xen toolstack to save the pages to file. Am I correct?
> You are using an older tree with a patch series based on a newer tree.
>
> So I would recommend you to move to a newer tree. If it is not possible,
> please test that hibernation works on baremetal.
I think the suspend/resume in guest is working, cause I can use 
pause/unpause command in toolstack to suspend/resume guest without 
problem. I can also see the suspend/resume kernel messages from guest's 
console. The only problem is it's can not resume from restore.
One thing that confused me is that the kernel's hibernation means the 
guest kernel will save the memory state to disk and power off VM at 
last. The guest will also take care of the memory restore itself. But I 
do not see the save/restore on xen works that way. So my question is why 
it requires hibernation (aka. suspend to disk) instead of the real 
suspend (aka. suspend to RAM and standby)?

> Regards,
>
> [1] https://lists.96boards.org/pipermail/dev/2016-May/000933.html
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