On Mon, Jan 24, 2022 at 05:01:04PM +0100, Jan Beulich wrote:
> On 24.01.2022 16:23, Roger Pau Monne wrote:
> > RMRRs are setup ahead of populating the p2m and hence the ASSERT when
> > populating the low 1MB needs to be relaxed when it finds an existing
> > entry: it's either RAM or a RMRR resulting from the IOMMU setup.
> >
> > Rework the logic a bit and introduce a local mfn variable in order to
> > assert that if the gfn is populated and not RAM it is an identity map.
> >
> > Fixes: 6b4f6a31ac ('x86/PVH: de-duplicate mappings for first Mb of Dom0
> > memory')
> > Signed-off-by: Roger Pau Monné <roger....@citrix.com>
>
> Reviewed-by: Jan Beulich <jbeul...@suse.com>
> albeit ...
>
> > --- a/xen/arch/x86/hvm/dom0_build.c
> > +++ b/xen/arch/x86/hvm/dom0_build.c
> > @@ -466,11 +466,17 @@ static int __init pvh_populate_p2m(struct domain *d)
> > for ( i = rc = 0; i < MB1_PAGES; ++i )
> > {
> > p2m_type_t p2mt;
> > + mfn_t mfn;
> >
> > - if ( mfn_eq(get_gfn_query(d, i, &p2mt), INVALID_MFN) )
> > + mfn = get_gfn_query(d, i, &p2mt);
>
> ... preferably with this becoming the initializer of the variable then
> and ...
>
> > + if ( mfn_eq(mfn, INVALID_MFN) )
> > rc = set_mmio_p2m_entry(d, _gfn(i), _mfn(i), PAGE_ORDER_4K);
> > - else
> > - ASSERT(p2mt == p2m_ram_rw);
> > + else if ( p2mt != p2m_ram_rw && !mfn_eq(mfn, _mfn(i)) )
> > + /*
> > + * If the p2m entry is already set it must belong to a
> > RMRR and
> > + * already be identity mapped, or be a RAM region.
> > + */
> > + ASSERT_UNREACHABLE();
>
> ... (not just preferably) indentation reduced by a level here. (I wonder
> why you didn't simply extend the existing ASSERT() - ASSERT_UNREACHABLE()
> is nice in certain cases, but the expression it logs is entirely unhelpful
> for disambiguating the reason without looking at the source.)
Indeed, that's better. Sorry about the indentation, not sure what my
editor has done here.
Thanks, Roger.
