Re: [Xen-devel] [PATCH v12 5/6] x86/ioreq server: Asynchronously reset outstanding p2m_ioreq_server entries.

[Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>]

On 4/7/2017 7:28 PM, Jan Beulich wrote:
> > > > On 07.04.17 at 12:50, <yu.c.zhang@xxxxxxxxxxxxxxx> wrote:
> > On 4/7/2017 6:28 PM, George Dunlap wrote:
> > > On 07/04/17 11:14, Yu Zhang wrote:
> > > > On 4/7/2017 5:40 PM, Jan Beulich wrote:
> > > > > > > > On 06.04.17 at 17:53, <yu.c.zhang@xxxxxxxxxxxxxxx> wrote:
> > > > > > --- a/xen/arch/x86/mm/p2m-ept.c
> > > > > > +++ b/xen/arch/x86/mm/p2m-ept.c
> > > > > > @@ -544,6 +544,12 @@ static int resolve_misconfig(struct p2m_domain
> > > > > > *p2m, unsigned long gfn)
> > > > > >                         e.ipat = ipat;
> > > > > >                         if ( e.recalc && p2m_is_changeable(e.sa_p2mt) )
> > > > > >                         {
> > > > > > +                         if ( e.sa_p2mt == p2m_ioreq_server )
> > > > > > +                         {
> > > > > > +                             ASSERT(p2m->ioreq.entry_count > 0);
> > > > > > +                             p2m->ioreq.entry_count--;
> > > > > > +                         }
> > > > > > +
> > > > > >                              e.sa_p2mt = p2m_is_logdirty_range(p2m, gfn
> > > > > > + i, gfn + i)
> > > > > >                                          ? p2m_ram_logdirty : p2m_ram_rw;
> > > > > I don't think this can be right: Why would it be valid to change the
> > > > > type from p2m_ioreq_server to p2m_ram_rw (or p2m_ram_logdirty)
> > > > > here, without taking into account further information? This code
> > > > > can run at any time, not just when you want to reset things. So at
> > > > > the very least there is a check missing whether a suitable ioreq
> > > > > server still exists (and only if it doesn't you want to do the type
> > > > > reset).
> > > > Also I do not think we need to check if a suitable ioreq server still
> > > > exists. We have guaranteed
> > > > in our patch that no new ioreq server will be mapped as long as the p2m
> > > > table is not clean. :)
> > > Jan is saying that you should only change ioreq_server -> ram if there
> > > is *not* an ioreq server; and that if this is called with an ioreq
> > > server still active, then it must be some other change you're looking at.
> > >
> > > The problem, though, is that misconfiguration happens in many
> > > circumstances.  Grep for "memory_type_changed()" -- each of those
> > > results in a recalculation of the entire p2m, which will (in the current
> > > code) wipe out any ioreq_server entries.
> > Well, I'm not aware that other actions besides the logdirty will cause the 
> > reset.
> > But if that would happen, will below change solve this?
> >
> > @@ -546,12 +546,16 @@ static int resolve_misconfig(struct p2m_domain *p2m, 
> > unsigned long gfn)
> >                        {
> >                             if ( e.sa_p2mt == p2m_ioreq_server )
> >                             {
> > -                             ASSERT(p2m->ioreq.entry_count > 0);
> > -                             p2m->ioreq.entry_count--;
> > +                             if ( p2m->ioreq.server == NULL )
> > +                             {
> > +                                 ASSERT(p2m->ioreq.entry_count > 0);
> > +                                 p2m->ioreq.entry_count--;
> > +                                 e.sa_p2mt = p2m_ram_rw;
> > +                             }
> >                             }
> > -
> > -                         e.sa_p2mt = p2m_is_logdirty_range(p2m, gfn + i, gfn + 
> > i)
> > -                                     ? p2m_ram_logdirty : p2m_ram_rw;
> > +                         else
> > +                             e.sa_p2mt = p2m_is_logdirty_range(p2m, gfn + i, 
> > gfn + i)
> > +                                         ? p2m_ram_logdirty : p2m_ram_rw;
> Now you _never_ change away from ioreq-server, you only adjust
> the counter.
Oh right.

Then sth. like:

diff --git a/xen/arch/x86/mm/p2m-ept.c b/xen/arch/x86/mm/p2m-ept.c
index ecd5ceb..b960a1d 100644
--- a/xen/arch/x86/mm/p2m-ept.c
+++ b/xen/arch/x86/mm/p2m-ept.c
@@ -542,7 +542,10 @@ static int resolve_misconfig(struct p2m_domain 
*p2m, unsigned long gfn)
                                                _mfn(e.mfn), 0, &ipat,
                                                e.sa_p2mt == 
p2m_mmio_direct);
                     e.ipat = ipat;
-                    if ( e.recalc && p2m_is_changeable(e.sa_p2mt) )
+                    if ( e.recalc &&
+                         (p2m_check_changeable(e.sa_p2mt) ||
+                          (e.sa_p2mt == p2m_ioreq_server &&
+                           p2m->ioreq.server == NULL)) )
                     {
                          if ( e.sa_p2mt == p2m_ioreq_server )
                          {
diff --git a/xen/arch/x86/mm/p2m-pt.c b/xen/arch/x86/mm/p2m-pt.c
index 4b2ff9e..1c600b1 100644
--- a/xen/arch/x86/mm/p2m-pt.c
+++ b/xen/arch/x86/mm/p2m-pt.c
@@ -442,7 +442,8 @@ static int do_recalc(struct p2m_domain *p2m, 
unsigned long gfn)
             P2M_DEBUG("bogus recalc leaf at d%d:%lx:%u\n",
                       p2m->domain->domain_id, gfn, level);
         p2mt_old = p2m_flags_to_type(l1e_get_flags(e));
-        if ( p2m_is_changeable(p2mt_old) )
+        if ( p2m_check_changeable(p2mt_old) ||
+             (p2mt_old == p2m_ioreq_server && p2m->ioreq.server == NULL) )
         {
             unsigned long mask = ~0UL << (level * PAGETABLE_ORDER);
             p2m_type_t p2mt = p2m_is_logdirty_range(p2m, gfn & mask, 
gfn | ~mask)
But as you can see. I used p2m_check_changeable() here.

Yu
> Jan
>
>
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