Xen devel - May 2008 - [Patch 4/4]: Xend interface for HVM S3

[Patch 4/4]: Xend interface for HVM S3
   - extend "xm resume <domid>" to be able to S3 resume HVM
domain.
   - when user issue "xm resume" command for HVM domain, xend will use
     xc lib API to call HVMOP_s3_resume hypercall.
 
 Note: it may not appropriate use xm resume for HVM s3, since xm resume
 is originally designed for save/restor purpose. It will be fine that
 xend maintainer find another place to put this code.
 
 Signed-off-by: Yu Ke <ke.yu@intel.com>
 Signed-off-by: Ke Liping <liping.ke@intel.com>



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Ke, Liping writes ("[Xen-devel] [Patch 4/4]: Xend interface for HVM
S3"):
>  [Patch 4/4]: Xend interface for HVM S3
>    - extend "xm resume <domid>" to be able to S3 resume HVM
domain.
>    - when user issue "xm resume" command for HVM domain, xend
will use
>      xc lib API to call HVMOP_s3_resume hypercall.
>  
>  Note: it may not appropriate use xm resume for HVM s3, since xm resume
>  is originally designed for save/restor purpose. It will be fine that
>  xend maintainer find another place to put this code.
If you want to reuse `xm resume'' for this you need to think about the
interactions with the existing `xm suspend'' and `xm resume''. 
What
combination of states are permissible, what transitions exist, and how
are they triggered ?

What if the guest is in the middle of going into one kind of suspend
when a request arrives to put it into a different kind of suspend ?
(Users often make multiple similar requests if they think the first
request isn''t working.)

Ian.

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Ian Jackson wrote:
> Ke, Liping writes ("[Xen-devel] [Patch 4/4]: Xend interface for HVM
> S3"): 
>>  [Patch 4/4]: Xend interface for HVM S3
>>    - extend "xm resume <domid>" to be able to S3 resume
HVM domain.
>>    - when user issue "xm resume" command for HVM domain, xend
will
>>      use xc lib API to call HVMOP_s3_resume hypercall.
>> 
>>  Note: it may not appropriate use xm resume for HVM s3, since xm
>>  resume is originally designed for save/restor purpose. It will be
>>  fine that xend maintainer find another place to put this code.
> 
> If you want to reuse `xm resume'' for this you need to think about
the
> interactions with the existing `xm suspend'' and `xm
resume''.  What
> combination of states are permissible, what transitions exist, and how
> are they triggered ?
Since hvm suspend is initiated by HVM guest, so only xm resume entry
is reused here.
> 
> What if the guest is in the middle of going into one kind of suspend
> when a request arrives to put it into a different kind of suspend ?
> (Users often make multiple similar requests if they think the first
> request isn''t working.)
Currently it will do HVM_S3_Resume when we detect it is hvm domain
in  domain_resume temporarially. I think it is a temporary solution.
I think there are only two combinations: if it is save, resume -> restore.
Otherwise, resume->s3 wake up for HVM.
So do you think which way is better, reuse xm resume or not?
> Ian.

Thanks a lot!
Regards,
Criping

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Ke, Liping writes ("RE: [Xen-devel] [Patch 4/4]: Xend interface for HVM
S3"):
> Since hvm suspend is initiated by HVM guest, so only xm resume entry
> is reused here.
I see.  That seems ... odd.
> > What if the guest is in the middle of going into one kind of suspend
> > when a request arrives to put it into a different kind of suspend ?
> > (Users often make multiple similar requests if they think the first
> > request isn''t working.)
> 
> Currently it will do HVM_S3_Resume when we detect it is hvm domain
> in  domain_resume temporarially. I think it is a temporary solution.
> I think there are only two combinations: if it is save, resume ->
restore.
> Otherwise, resume->s3 wake up for HVM.
Can the guest be saved (with `xm suspend'') while it is suspending
(into HVM S3) ?  If so then you may have to resume it twice ...
> So do you think which way is better, reuse xm resume or not?
Sad though I am to say it, I think we need yet another kind of
resumption/restoration/restarting/etc.

Ian.

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On 8/5/08 11:13, "Ian Jackson" <Ian.Jackson@eu.citrix.com>
wrote:
>> So do you think which way is better, reuse xm resume or not?
> 
> Sad though I am to say it, I think we need yet another kind of
> resumption/restoration/restarting/etc.
This has always been the problem with the virtual S3 support. Actually
usefully integrating it into the save/restore is the hard bit.

 -- Keir



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On Thu, 8 May 2008, Keir Fraser wrote:
> On 8/5/08 11:13, "Ian Jackson" <Ian.Jackson@eu.citrix.com>
wrote:
>
> >> So do you think which way is better, reuse xm resume or not?
> >
> > Sad though I am to say it, I think we need yet another kind of
> > resumption/restoration/restarting/etc.
>
> This has always been the problem with the virtual S3 support. Actually
> usefully integrating it into the save/restore is the hard bit.
Is there currently a practical use why virtual S3 is prefered over the
save command? Is it more gracefully?

(or is the actual usage the other way around, when a user initiates the
S3)


Stefan


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> Is there currently a practical use why virtual S3 is prefered over the
> save command? Is it more gracefully?
They have quite different purposes.

One use for guest S3 is in integrating it into a save/restore so that
the guest isn''t so surprised when it wakes up and finds that time has
suddenly warped forward. In practice, Linux/Windows seem to cope just
fine without passing through S3. Doing so might be cleaner, but at the
risk of tickling guest operating system S3 bugs 

Guest S3 is also useful in the context of PCI device passthrough, where
its necessary to get the device into a safe state.
> (or is the actual usage the other way around, when a user initiates
the
> S3)
The guest must initiate S3, but you can typically prod it into doing so
via the ''lid switch''.

Ian
> 
> 
> Stefan
> 
> 
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Ian Pratt writes ("RE: [Xen-devel] [Patch 4/4]: Xend interface for HVM
S3"):
> Guest S3 is also useful in the context of PCI device passthrough, where
> its necessary to get the device into a safe state.
S3 doesn''t involve writing a memory image to disk; it''s
`suspend to
RAM'' - more like xm pause than xm save.  S4 is suspend to disk, like
xm save.

xm pause is certainly a lot simpler than the full-on ACPI S3 support.
I think the latter is, as Ian says, mainly useful when the guest has
direct access to hardware devices.  If you want to put the physical
machine into S3 or S4 then you need cooperation from all the domains
which own the hardware.

Ian.

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[PATCH 4/4]: Xend interface for HVM S3
  - extend "xm trigger <domid> s3resume" to be able to S3 resume
HVM domain.
  - when user issue "xm trigger" command for HVM domain, xend will use
xc
    lib API to call XEN_DOMCTL_SENDTRIGGER_S3RESUME domctl hypercall.
  - add s3_suspended state for HVM domain

Note: S3 suspend is initiated from HVM guest itself and resumed from
xm trigger command. We also add a new HVM state: s3_suspended, so that
save/restore now could work with a s3_suspended domain.

Signed-off-by: Yu Ke <ke.yu@intel.com>
Signed-off-by: Ke Liping <liping.ke@intel.com


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