Re: [Xen-devel] [PATCH v8 3/3] tools/libxc: use superpages during restore of HVM guest

[Olaf Hering <olaf@xxxxxxxxx>]

On Fri, Sep 01, Olaf Hering wrote:

> +static int x86_hvm_populate_pfns(struct xc_sr_context *ctx, unsigned count,

> +            /*
> +             * If this next pfn is within another 1GB superpage it is 
> required
> +             * to scan the entire previous superpage because there might be
> +             * holes between max_pfn and the end of the superpage.
> +             */
> +            if ( idx1G_prev != idx1G )
> +            {
> +                order = SUPERPAGE_1GB_SHIFT;
> +                max_pfn = (((max_pfn >> order) + 1) << order) - 1;
> +            }
> +            if ( x86_hvm_punch_hole(ctx, max_pfn) == false )


And thinking about this part: with this variant it is still possible
that Over-allocation happens. If the previous pfn was within a 2MB
range, and this pfn is in another 2MB range, then the hole after max_pfn
would not be covered. This part needs an 'else' with
SUPERPAGE_2MB_SHIFT.

This "reset to max" may trigger a bug in xc_sr_test_and_clear_bit(). It
has to check the size of the bitmap, just as xc_sr_test_bit() does.

Olaf

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