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Re: [Qemu-devel] [PATCH V2 5/5] vga-cirrus: Workaround during restore wh
From: |
Avi Kivity |
Subject: |
Re: [Qemu-devel] [PATCH V2 5/5] vga-cirrus: Workaround during restore when using Xen. |
Date: |
Thu, 05 Jan 2012 17:19:58 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:8.0) Gecko/20111115 Thunderbird/8.0 |
On 01/05/2012 04:34 PM, Stefano Stabellini wrote:
> On Thu, 5 Jan 2012, Avi Kivity wrote:
> > On 01/05/2012 03:17 PM, Stefano Stabellini wrote:
> > > > > The "solution" I am proposing is introducing an early_savevm set of
> > > > > save/restore functions so that at restore time we can get to know at
> > > > > what address the videoram is mapped into the guest address space.
> > > > > Once we
> > > > > know the address we can remap it into qemu's address space and/or
> > > > > move it
> > > > > to another guest physical address.
> > > >
> > > > Why can we not simply track it? For every MemoryRegion, have a field
> > > > called xen_address which tracks its location in the Xen address space
> > > > (as determined by the last call to xen_set_memory or qemu_ram_alloc).
> > > > xen_address would be maintained by callbacks called from the memory API
> > > > into xen-all.c.
> > >
> > > Nice and simple, I like it.
> > > However we would still need an early_savevm mechanism to save and restore
> > > the
> > > MemoryRegions, unless they already gets saved and restored somehow?
> >
> > MemoryRegions are instantiated by the devices, so they should be there
> > (creating a MemoryRegion == calling qemu_ram_alloc() in the old days)
>
> If the MemoryRegions are re-created by the devices, then we need another
> mechanism to find out where the videoram is.
> What I am saying is that the suggestion of having a xen_address field
> for every MemoryRegion would make the code cleaner but it would not
> solve the save/restore issue described in the previous email.
Okay, I think I understand now.
You're not really allocating memory on restore, you're attaching to
already allocated memory, and you need a handle to it, passed from the
save side.
One way is to add early-save/restore like you suggest. Another is to
make the attach late. Can we defer it until after restore is complete
and we know everything?
This involves:
- adding vmstate to xen-all.c so it can migrate the xen vram address
- making sure the memory core doesn't do mappings during restore (can be
done by wrapping restore with
memory_region_transaction_begin()/memory_region_transaction_commit();
beneficial to normal qemu migrations as well)
- updating the mapped address during restore
I think this is cleaner than introducing a new migration stage, but the
implementation may prove otherwise.
> >
> > xen_register_framebuffer() is slightly less hacky.
>
> I agree, however xen_register_framebuffer is called after
> memory_region_init_ram, so the allocation would have been made already.
xen_ram_alloc(MemoryRegion *mr)
{
if (in_restore && mr == framebuffer && !framebuffer_addr_known) {
return;
}
}
xen_framebuffer_address_post_load()
{
framebuffer_addr_known = true;
if (framebuffer) {
framebuffer->xen_address = framebuffer_addr;
}
}
(ugly way of avoiding a dependency, but should work)
--
error compiling committee.c: too many arguments to function
- Re: [Qemu-devel] [PATCH V2 5/5] vga-cirrus: Workaround during restore when using Xen., Stefano Stabellini, 2012/01/04
- Re: [Qemu-devel] [PATCH V2 5/5] vga-cirrus: Workaround during restore when using Xen., Avi Kivity, 2012/01/04
- Re: [Qemu-devel] [PATCH V2 5/5] vga-cirrus: Workaround during restore when using Xen., Stefano Stabellini, 2012/01/05
- Re: [Qemu-devel] [PATCH V2 5/5] vga-cirrus: Workaround during restore when using Xen., Avi Kivity, 2012/01/05
- Re: [Qemu-devel] [PATCH V2 5/5] vga-cirrus: Workaround during restore when using Xen., Stefano Stabellini, 2012/01/05
- Re: [Qemu-devel] [PATCH V2 5/5] vga-cirrus: Workaround during restore when using Xen., Avi Kivity, 2012/01/05
- Re: [Qemu-devel] [PATCH V2 5/5] vga-cirrus: Workaround during restore when using Xen., Stefano Stabellini, 2012/01/05
- Re: [Qemu-devel] [PATCH V2 5/5] vga-cirrus: Workaround during restore when using Xen.,
Avi Kivity <=
- Re: [Qemu-devel] [PATCH V2 5/5] vga-cirrus: Workaround during restore when using Xen., Stefano Stabellini, 2012/01/05
- Re: [Qemu-devel] [PATCH V2 5/5] vga-cirrus: Workaround during restore when using Xen., Avi Kivity, 2012/01/05
- Re: [Qemu-devel] [PATCH V2 5/5] vga-cirrus: Workaround during restore when using Xen., Stefano Stabellini, 2012/01/05
- Re: [Qemu-devel] [PATCH V2 5/5] vga-cirrus: Workaround during restore when using Xen., Avi Kivity, 2012/01/05
- Re: [Qemu-devel] [PATCH V2 5/5] vga-cirrus: Workaround during restore when using Xen., Jan Kiszka, 2012/01/05
- Re: [Qemu-devel] [PATCH V2 5/5] vga-cirrus: Workaround during restore when using Xen., Stefano Stabellini, 2012/01/06
- Re: [Qemu-devel] [PATCH V2 5/5] vga-cirrus: Workaround during restore when using Xen., Jan Kiszka, 2012/01/06
- Re: [Qemu-devel] [PATCH V2 5/5] vga-cirrus: Workaround during restore when using Xen., Stefano Stabellini, 2012/01/06
- Re: [Qemu-devel] [PATCH V2 5/5] vga-cirrus: Workaround during restore when using Xen., Avi Kivity, 2012/01/08
- Re: [Qemu-devel] [PATCH V2 5/5] vga-cirrus: Workaround during restore when using Xen., Stefano Stabellini, 2012/01/09