Re: [Xen-devel] [PATCH RFC 27/55] x86_64/mm: drop lXe_to_lYe invocations from setup_m2p_table

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Mon, Mar 18, 2019 at 09:14:38PM +0000, Nuernberger, Stefan wrote:
> On Thu, 2019-02-07 at 16:44 +0000, Wei Liu wrote:
> > Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
> > ---
> >  xen/arch/x86/x86_64/mm.c | 16 ++++++++++++----
> >  1 file changed, 12 insertions(+), 4 deletions(-)
> > 
> > diff --git a/xen/arch/x86/x86_64/mm.c b/xen/arch/x86/x86_64/mm.c
> > index 0b85961105..216f97c95f 100644
> > --- a/xen/arch/x86/x86_64/mm.c
> > +++ b/xen/arch/x86/x86_64/mm.c
> > @@ -400,11 +400,13 @@ static int setup_m2p_table(struct
> > mem_hotadd_info *info)
> >      l2_pgentry_t *pl2e = NULL, *l2_ro_mpt = NULL;
> >      l3_pgentry_t *l3_ro_mpt = NULL;
> >      int ret = 0;
> > -    mfn_t l2_ro_mpt_mfn;
> > +    mfn_t l2_ro_mpt_mfn, l3_ro_mpt_mfn;
> >  
> >      ASSERT(l4e_get_flags(idle_pg_table[l4_table_offset(RO_MPT_VIRT_S
> > TART)])
> >              & _PAGE_PRESENT);
> > -    l3_ro_mpt =
> > l4e_to_l3e(idle_pg_table[l4_table_offset(RO_MPT_VIRT_START)]);
> > +    l3_ro_mpt_mfn = l4e_get_mfn(idle_pg_table[l4_table_offset(
> > +                                        RO_MPT_VIRT_START)]);
> > +    l3_ro_mpt = map_xen_pagetable_new(l3_ro_mpt_mfn);
> >  
> >      smap = (info->spfn & (~((1UL << (L2_PAGETABLE_SHIFT - 3)) -1)));
> >      emap = ((info->epfn + ((1UL << (L2_PAGETABLE_SHIFT - 3)) - 1 ))
> > &
> > @@ -459,8 +461,13 @@ static int setup_m2p_table(struct
> > mem_hotadd_info *info)
> >                    _PAGE_PSE));
> >              if ( l3e_get_flags(l3_ro_mpt[l3_table_offset(va)]) &
> >                _PAGE_PRESENT )
> > -                pl2e = l3e_to_l2e(l3_ro_mpt[l3_table_offset(va)]) +
> > -                  l2_table_offset(va);
> > +            {
> > +                UNMAP_XEN_PAGETABLE_NEW(l2_ro_mpt);
> > +                l2_ro_mpt_mfn =
> > l3e_get_mfn(l3_ro_mpt[l3_table_offset(va)]);
> > +                l2_ro_mpt = map_xen_pagetable_new(l2_ro_mpt_mfn);
> > +                ASSERT(l2_ro_mpt);
> 
> Do we need this assert here? What are the possibilities to recover from
> that situation? I think this should be BUG_ON or it should at least
> return through the error path.

I'm not too fussed. This is early initialisation of xen. If this doesn't
work, all bets are off.

Wei.

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