[Xen-devel] [PATCH RFC] x86/ioreq server: Optimize p2m cleaning up code in p2m_finish_type_change().

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

Previously, p2m_finish_type_change() is triggered to iterate and
clean up the p2m table when an ioreq server unmaps from memory type
HVMMEM_ioreq_server. And the current iteration number is set to 256
And after these iterations, hypercall pre-emption is checked.

But it is likely that no p2m change is performed for the just finished
iterations, which means p2m_finish_type_change() will return quite
soon. So in such scenario, we can allow the p2m iteration to continue,
without checking the hypercall pre-emption.

Signed-off-by: Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>
---
Note: this patch shall only be accepted after previous x86/ioreq server
patches be merged.

Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Cc: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
---
 xen/arch/x86/hvm/dm.c     | 5 ++++-
 xen/arch/x86/mm/p2m.c     | 9 ++++++++-
 xen/include/asm-x86/p2m.h | 2 +-
 3 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/xen/arch/x86/hvm/dm.c b/xen/arch/x86/hvm/dm.c
index d72b7bd..3aa1286 100644
--- a/xen/arch/x86/hvm/dm.c
+++ b/xen/arch/x86/hvm/dm.c
@@ -411,14 +411,17 @@ static int dm_op(domid_t domid,
             while ( read_atomic(&p2m->ioreq.entry_count) &&
                     first_gfn <= p2m->max_mapped_pfn )
             {
+                bool changed = false;
+
                 /* Iterate p2m table for 256 gfns each time. */
                 p2m_finish_type_change(d, _gfn(first_gfn), 256,
-                                       p2m_ioreq_server, p2m_ram_rw);
+                                       p2m_ioreq_server, p2m_ram_rw, &changed);
 
                 first_gfn += 256;
 
                 /* Check for continuation if it's not the last iteration. */
                 if ( first_gfn <= p2m->max_mapped_pfn &&
+                     changed &&
                      hypercall_preempt_check() )
                 {
                     rc = -ERESTART;
diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
index 0daaa86..b171a4b 100644
--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -1034,12 +1034,13 @@ void p2m_change_type_range(struct domain *d,
 /* Synchronously modify the p2m type for a range of gfns from ot to nt. */
 void p2m_finish_type_change(struct domain *d,
                             gfn_t first_gfn, unsigned long max_nr,
-                            p2m_type_t ot, p2m_type_t nt)
+                            p2m_type_t ot, p2m_type_t nt, bool *changed)
 {
     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;
+    bool is_changed = false;
 
     ASSERT(ot != nt);
     ASSERT(p2m_is_changeable(ot) && p2m_is_changeable(nt));
@@ -1052,12 +1053,18 @@ void p2m_finish_type_change(struct domain *d,
         get_gfn_query_unlocked(d, gfn, &t);
 
         if ( t == ot )
+        {
             p2m_change_type_one(d, gfn, t, nt);
+            is_changed = true;
+        }
 
         gfn++;
     }
 
     p2m_unlock(p2m);
+
+    if ( changed )
+        *changed = is_changed;
 }
 
 /*
diff --git a/xen/include/asm-x86/p2m.h b/xen/include/asm-x86/p2m.h
index 0e670af..2e02538 100644
--- a/xen/include/asm-x86/p2m.h
+++ b/xen/include/asm-x86/p2m.h
@@ -615,7 +615,7 @@ int p2m_change_type_one(struct domain *d, unsigned long gfn,
 void p2m_finish_type_change(struct domain *d,
                             gfn_t first_gfn,
                             unsigned long max_nr,
-                            p2m_type_t ot, p2m_type_t nt);
+                            p2m_type_t ot, p2m_type_t nt, bool *changed);
 
 /* Report a change affecting memory types. */
 void p2m_memory_type_changed(struct domain *d);
-- 
1.9.1


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