[Xen-devel] [PATCH V12 5/5] p2m: change_type_range: Only invalidate mapped gfns

[Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>]

change_type_range() invalidates gfn ranges to lazily change the type
of a range of gfns, and also modifies the logdirty rangesets of that
p2m. At the moment, it clips both down by the hostp2m.

While this will result in correct behavior, it's not entirely efficient,
since invalidated entries outside that range will, on fault, simply be
modified back to "empty" before faulting normally again.

Separate out the calculation of the two ranges. Keep using the
hostp2m's max_mapped_pfn to clip the logdirty ranges, but use the
current p2m's max_mapped_pfn to further clip the invalidation range
for alternate p2ms.

Signed-off-by: George Dunlap <george.dunlap@xxxxxxxxxx>
Signed-off-by: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
Tested-by: Tamas K Lengyel <tamas@xxxxxxxxxxxxx>
Acked-by: George Dunlap <george.dunlap@xxxxxxxxxx>

---
CC: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
CC: Jan Beulich <jbeulich@xxxxxxxx>
CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CC: Wei Liu <wei.liu2@xxxxxxxxxx>
CC: "Roger Pau Monné" <roger.pau@xxxxxxxxxx>

---
Changes since V11:
 - Made the patch fit on top of patch 4 (it no longer applied
   cleanly).
 - Added George's Acked-by.
---
 xen/arch/x86/mm/p2m.c | 58 +++++++++++++++++++++++++++++++++++++--------------
 1 file changed, 42 insertions(+), 16 deletions(-)

diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
index f552fd5..3f6bf6f 100644
--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -1007,18 +1007,28 @@ static void change_type_range(struct p2m_domain *p2m,
                               unsigned long start, unsigned long end_exclusive,
                               p2m_type_t ot, p2m_type_t nt)
 {
+    unsigned long invalidate_start, invalidate_end;
     struct domain *d = p2m->domain;
     const unsigned long host_max_pfn = p2m_get_hostp2m(d)->max_mapped_pfn;
     unsigned long end = end_exclusive - 1;
+    const unsigned long max_pfn = p2m->max_mapped_pfn;
     int rc = 0;
 
     /*
-     * Always clip the rangeset down to the host p2m. This is probably not
-     * the right behavior. This should be revisited later, but for now post a
-     * warning.
+     * If we have an altp2m, the logdirty rangeset range needs to
+     * match that of the hostp2m, but for efficiency, we want to clip
+     * down the the invalidation range according to the mapped values
+     * in the altp2m. Keep track of and clip the ranges separately.
+     */
+    invalidate_start = start;
+    invalidate_end   = end;
+
+    /*
+     * Clip down to the host p2m. This is probably not the right behavior.
+     * This should be revisited later, but for now post a warning.
      */
     if ( unlikely(end > host_max_pfn) )
-        end = host_max_pfn;
+        end = invalidate_end = host_max_pfn;
 
     if ( start >= host_max_pfn )
         printk(XENLOG_G_WARNING "Dom%d logdirty rangeset clipped to 
max_mapped_pfn\n",
@@ -1028,21 +1038,37 @@ static void change_type_range(struct p2m_domain *p2m,
     if ( start > end )
         return;
 
+    if ( p2m_is_altp2m(p2m) )
+        invalidate_end = min(invalidate_end, max_pfn);
+
     /*
-     * If all valid gfns are in the invalidation range, just do a
-     * global type change. Otherwise, invalidate only the range we
-     * need.
+     * If the p2m is empty, or the range is outside the currently
+     * mapped range, no need to do the invalidation; just update the
+     * rangeset.
      */
-    if ( !start && end >= p2m->max_mapped_pfn )
-        p2m->change_entry_type_global(p2m, ot, nt);
-    else
-        rc = p2m->change_entry_type_range(p2m, ot, nt, start, end);
-
-    if ( rc )
+    if ( invalidate_start < invalidate_end )
     {
-        printk(XENLOG_G_ERR "Error %d changing Dom%d GFNs [%lx,%lx) from %d to 
%d\n",
-               rc, d->domain_id, start, end_exclusive, ot, nt);
-        domain_crash(d);
+        /*
+         * If all valid gfns are in the invalidation range, just do a
+         * global type change. Otherwise, invalidate only the range
+         * we need.
+         *
+         * NB that invalidate_end can't logically be >max_pfn at this
+         * point. If this changes, the == will need to be changed to
+         * >=.
+         */
+        ASSERT(invalidate_end <= max_pfn);
+        if ( !invalidate_start && invalidate_end == max_pfn)
+            p2m->change_entry_type_global(p2m, ot, nt);
+        else
+            rc = p2m->change_entry_type_range(p2m, ot, nt,
+                                              invalidate_start, 
invalidate_end);
+        if ( rc )
+        {
+            printk(XENLOG_G_ERR "Error %d changing Dom%d GFNs [%lx,%lx] from 
%d to %d\n",
+                   rc, d->domain_id, invalidate_start, invalidate_end, ot, nt);
+            domain_crash(d);
+        }
     }
 
     switch ( nt )
-- 
2.7.4


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