Re: [Xen-devel] [PATCH v6 3/3] tools/libxc: use superpages during restore of HVM guest

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Wed, Aug 30, 2017 at 04:27:19PM +0200, Olaf Hering wrote:
> On Wed, Aug 30, Wei Liu wrote:
> 
> > As far as I can tell the algorithm in the patch can't handle:
> > 
> > 1. First pfn in a batch points to start of second 1G address space
> > 2. Second pfn in a batch points to a page in the middle of first 1G
> > 3. Guest can only use 1G ram
> 
> In which way does it not handle it? Over-allocation is supposed to be
> handled by the "ctx->restore.tot_pages + sp->count >
> ctx->restore.max_pages" checks. Do you mean the second 1G is allocated,
> then max_pages is reached, and allocation in other areas is not possible
> anymore?

Yes.

> Can this actually happen with the available senders? If not, this is
> again the missing memory map.
> 

Probably not now, but as said, you shouldn't rely on the structure of
the stream unless it is stated in the spec.

And it can definitely happen with post-copy algorithm.

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