RE: [Xen-devel] [PATCH 0/4] HVM Virtual S3

["Ke, Liping" <liping.ke@xxxxxxxxx>]

Ian Pratt wrote:
>> The main idea is:
>> - emulate ACPI PM1A control resiger in QEMU to capture guest S3
>> request 
>> - when QEMU capture guest S3 request, it call hypercall to trap to
>> Xen 
>> - Xen will suspend HVM by reseting all vcpus
>> - on resume, "xm resume" will call hypercall to trap to Xen
>> - Xen will resume HVM by setting HVM vcpu EIP to 0xfff0, cs base to
>>   0xf0000, and also set other related registers/msr to the correct
>>   value/attributes in realmode environment which will start from
>>   rombios post Entry code in realmode directly when resuming.
>> - rombios post code will start s3 resume by jumping to wakeup vector
>>   set by guest OS.
> 
> Have you checked save/restore works when the guest is in S3 state?
> This is essential for some of the server (as opposed to client) use
> cases for guest S3.
Yes, save/restore should work when guest is in S3 state. When S3_sleep,
domain is still alive, just only that VCPU is blocked. We'll do further test
on it these days.
> 
> [One thing to watch out for is that if the guest is in S3 it should be
> possible to skip the usual synchronization with PV drivers as they
> will already be shutdown.]
Yes, when guest is in S3, PV drivers should not deal with any synchronization
Jobs. When resume back, it returns back to work again.
> 
> 
> Further, do we actually need the s3 resume hypercall? Couldn't we just
> put the VCPUs and xen-emulated devices into the right state for resume
> at the end of s3 sleep and just leave the domain paused (i.e.
> unscheduled)?
As I can understand, when S3, HVM will perform like native-machine S3, 
all execution context are in memory When resume back, jump to the CS/EIP,
those vcpus resume execution normally.
Ke& Kevin, any coments here?

> 
> 
> Also, do you have plans to implement an "xm send-power-event" type
> thing that enables us to inform the guest of actions such as lid
> switch open/close, power cable in/out, power button pressed etc ?
Since now host S3 and HVM S3 is not integrated yet, I am not sure
whether those lid/cable/power button are appropriate to be involved with
Guest notification. Especially if we have multiple guest. Yet I think we must
consider it carefully as part of VMM PM solution :)
If both host and HVM is S3 done, when lid open,
Xen is back, host is back and then HVM is back. It is a possible senario?

> 
> Many Thanks,
> Ian


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