Re: [PATCH] tools/libs/guest: fix save and restore of pv domains after 32-bit de-support

[Juergen Gross <jgross@xxxxxxxx>]

On 07.06.21 13:01, Andrew Cooper wrote:
> On 07/06/2021 10:04, Juergen Gross wrote:
> > After 32-bit PV-guests have been security de-supported when not running
> > under PV-shim, the hypervisor will no longer be configured to support
> > those domains per default when not being built as PV-shim.
> >
> > Unfortunately libxenguest will fail saving or restoring a PV domain
> > due to this restriction, as it is trying to get the compat MFN list
> > even for 64 bit guests.
> >
> > Fix that by obtaining the compat MFN list only for 32-bit PV guests.
> >
> > Fixes: 1a0f2fe2297d122a08fe ("SUPPORT.md: Un-shimmed 32-bit PV guests are no longer 
> > supported")
> > Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> > ---
> >   tools/libs/guest/xg_sr_common_x86_pv.c | 1 +
> >   1 file changed, 1 insertion(+)
> >
> > diff --git a/tools/libs/guest/xg_sr_common_x86_pv.c 
> > b/tools/libs/guest/xg_sr_common_x86_pv.c
> > index cd33406aab..ad20461e2e 100644
> > --- a/tools/libs/guest/xg_sr_common_x86_pv.c
> > +++ b/tools/libs/guest/xg_sr_common_x86_pv.c
> > @@ -154,6 +154,7 @@ int x86_pv_map_m2p(struct xc_sr_context *ctx)
> >       ctx->x86.pv.compat_m2p_mfn0 = entries[0].mfn;
> >   #else
> >       /* 64 bit toolstacks need to ask Xen specially for it */
> > +    if ( ctx->x86.pv.levels == 3 )
> >       {
> >           struct xen_machphys_mfn_list xmml = {
> >               .max_extents = 1,
> This wants to encompass the whole ifdef block, to avoid having differing
> behaviour between compile widths.
>
> Also the comment next to compat_m2p_mfn0 wants adjusting to say "only
> set for 32bit PV guests".
Okay, together with Jan's suggestion this makes sense.


Juergen

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