Re: questions of vm save/restore on arm64

[Julien Grall <julien.grall@arm.com>]

Hello,

On 01/06/16 01:28, Chenxiao Zhao wrote:
>
>
> On 5/30/2016 4:40 AM, Stefano Stabellini wrote:
>> On Fri, 27 May 2016, Chenxiao Zhao wrote:
>>> Hi,
>>>
>>> My board is Hikey on which have octa-core of arm cortex-a53. I have
>>> applied patches [1] to try vm save/restore on arm.
>>> These patches originally do not working on arm64. I have made some
>>> changes based on patch set [2].
>>
>> Hello Chenxiao,
>>
>> thanks for your interest in Xen on ARM save/restore.
>
> Hi Stefano,
>
> Thanks for your advice.
>
> I found a possible reason that cause the restore failure is that xen
> always failed on p2m_lookup for guest domain.

Who is calling p2m_lookup?

>
> I called dump_p2m_lookup in p2m_look() and get the output like below:
>
> (XEN) dom1 IPA 0x0000000039001000

Looking at the memory layout (see include/public/arch-arm.h) 0x39001000 
is part of the magic region. It contains pages for the console, 
xenstore, memaccess (see the list in tools/libxc/xc_dom_arm.c).

0x39001000 is the base address of the xenstore page.

> (XEN) P2M @ 0000000801e7ce80 mfn:0x79f3a
> (XEN) Using concatenated root table 0
> (XEN) 1ST[0x0] = 0x0040000079f3c77f
> (XEN) 2ND[0x1c8] = 0x0000000000000000
>
> My question is:
>
> 1. who is responsible for restoring p2m table, Xen or guest kernel?

AFAIK, the toolstack is restoring the most of the memory.

> 2. After restore, the vm always get zero memory space, but there is no

What do you mean by "zero memory space"?

> error reported on the restore progress. Does the memory requested by the
> guest kernel or should be allocated early by hypervisor?

Bear in mind that the patch series you are working on is an RFC and the 
ARM64 was not supported. There might be some issue in the save/restore path.

For instance xc_clear_domain_page (tools/libxc/xc_sr_restore_arm.c) main 
return an error if the memory is not mapped. But the caller does not 
check the return value.

Regards,

-- 
Julien Grall

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