Re: [Qemu-devel] [PATCH v4 0/6] save/restore on Xen

[Stefano Stabellini]

On Fri, 20 Jan 2012, Jan Kiszka wrote:
> On 2012-01-20 18:20, Stefano Stabellini wrote:
> > Hi all,
> > this is the fourth version of the Xen save/restore patch series.
> > We have been discussing this issue for quite a while on #qemu and
> > qemu-devel:
> > 
> > 
> > http://marc.info/?l=qemu-devel&m=132346828427314&w=2
> > http://marc.info/?l=qemu-devel&m=132377734605464&w=2
> > 
> > 
> > A few different approaches were proposed to achieve the goal
> > of a working save/restore with upstream Qemu on Xen, however after
> > prototyping some of them I came up with yet another solution, that I
> > think leads to the best results with the less amount of code
> > duplications and ugliness.
> > Far from saying that this patch series is an example of elegance and
> > simplicity, but it is closer to acceptable anything else I have seen so
> > far.
> > 
> > What's new is that Qemu is going to keep track of its own physmap on
> > xenstore, so that Xen can be fully aware of the changes Qemu makes to
> > the guest's memory map at any time.
> > This is all handled by Xen or Xen support in Qemu internally and can be
> > used to solve our save/restore framebuffer problem.
> > 
> >>From the Qemu common code POV, we still need to avoid saving the guest's
> > ram when running on Xen, and we need to avoid resetting the videoram on
> > restore (that is a benefit to the generic Qemu case too, because it
> > saves few cpu cycles).
> 
> For my understanding: Refraining from the memset is required as the
> already restored vram would then be overwritten?

Yep

> Or what is the ordering
> of init, RAM restore, and initial device reset now?

RAM restore (done by Xen)

physmap rebuild (done by xen_hvm_init in qemu)
pc_init()
qemu_system_reset()
load_vmstate()