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[Xen-devel] Re: memsize for HVM save/restore

To: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Subject: [Xen-devel] Re: memsize for HVM save/restore
From: "Zhai, Edwin" <edwin.zhai@xxxxxxxxx>
Date: Tue, 27 Mar 2007 23:42:26 +0800
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, Ewan Mellor <ewan@xxxxxxxxxxxxx>, "Zhai, Edwin" <edwin.zhai@xxxxxxxxx>
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On Mon, Mar 26, 2007 at 07:31:33PM +0100, Keir Fraser wrote:
> On 26/3/07 04:13, "Zhai, Edwin" <edwin.zhai@xxxxxxxxx> wrote:
> > I don't think so.
> > Besides locating PFNs, memsize is also used in QEMU for other purpose, such 
> > as
> > bitmap allocation, dev init and map_foreign*. So memsize is a must for qemu
> > init.
> > 
> > See following code in xc_hvm_build:
> > if ( v_end > HVM_BELOW_4G_RAM_END )
> >     shared_page_nr = (HVM_BELOW_4G_RAM_END >> PAGE_SHIFT) - 1;
> > else
> >     shared_page_nr = (v_end >> PAGE_SHIFT) - 1;
> > 
> > So it's impossible to get memsize by saved PFNs when restore a big memory
> > guest.
> It can use the new XENMEM_maximum_gpfn hypercall for bitmap allocation. I'm

2 concerns:
1. xc_hvm_build use SCRATCH_PFN(0xFFFFF) to map shared_info, which would 
overwrite the true max_gpfn. So shall we add check in set_p2m_entry for this?

2. If qemu get the memsize from XENMEM_maximum_gpfn when restore, it's better 
do the same thing when create, i.e. remove the '-m' qemu command line.

> not sure what memsize would have to do with dev init. The map_foreign* is
> hidden behind mapcache which shouldn't need to know memsize (although if
> it's an issue of sizing buckets I suppose it can use XENMEM_maximum_gpfn).
>  -- Keir

best rgds,

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