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Re: [Xen-devel] [PATCH V4] x86/ioreq_server: Make p2m_finish_type_change actually work


On 11/05/17 12:12, Jan Beulich wrote:
On 12.05.17 at 04:42, <xiong.y.zhang@xxxxxxxxx> wrote:
Commit 6d774a951696 ("x86/ioreq server: synchronously reset outstanding
p2m_ioreq_server entries when an ioreq server unmaps") introduced
p2m_finish_type_change(), which was meant to synchronously finish a
previously initiated type change over a gpfn range.  It did this by
calling get_entry(), checking if it was the appropriate type, and then
calling set_entry().

Unfortunately, a previous commit (1679e0df3df6 "x86/ioreq server:
asynchronously reset outstanding p2m_ioreq_server entries") modified
get_entry() to always return the new type after the type change, meaning
that p2m_finish_type_change() never changed any entries.  Which means
when an ioreq server was detached and then re-attached (as happens in
XenGT on reboot) the re-attach failed.

Fix this by using the existing p2m-specific recalculation logic instead
of doing a read-check-write loop.

Fix: 'commit 6d774a951696 ("x86/ioreq server: synchronously reset
      outstanding p2m_ioreq_server entries when an ioreq server unmaps")'

Signed-off-by: Xiong Zhang <xiong.y.zhang@xxxxxxxxx>
Signed-off-by: Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>
Reviewed-by: George Dunlap <george.dunlap@xxxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
albeit I'm not overly happy with ...

+int p2m_finish_type_change(struct domain *d,
+                           gfn_t first_gfn, unsigned long max_nr)
     struct p2m_domain *p2m = p2m_get_hostp2m(d);
-    p2m_type_t t;
     unsigned long gfn = gfn_x(first_gfn);
     unsigned long last_gfn = gfn + max_nr - 1;
-    ASSERT(ot != nt);
-    ASSERT(p2m_is_changeable(ot) && p2m_is_changeable(nt));
+    int rc = 0;


     last_gfn = min(last_gfn, p2m->max_mapped_pfn);
     while ( gfn <= last_gfn )
-        get_gfn_query_unlocked(d, gfn, &t);
-        if ( t == ot )
-            p2m_change_type_one(d, gfn, t, nt);
+        rc = p2m->recalc(p2m, gfn);
+        /*
+         * ept->recalc could return 0/1/-ENOMEM. pt->recalc could return
+         * 0/-ENOMEM/-ENOENT, -ENOENT isn't an error as we are looping
+         * gfn here.
+         */
+        if ( rc == -ENOENT)

NIT: space missing before )

+            rc = 0;
+        else if ( rc < 0 )
+        {
+            gdprintk(XENLOG_ERR, "p2m->recalc failed! Dom%d gfn=%lx\n",
+                     d->domain_id, gfn);

... a message being logged here.

Also I'm sure it was pointed out before that if this is meant for
4.9 (which I assume it is) you should have Cc-ed Julien (now

Xiong Zhang, can you confirm this is meant for Xen 4.9?


Julien Grall

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