[Xen-devel] [PATCH V7 5/5] p2m: change_range_type: Only invalidate mapped gfns

[Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>]

change_range_type() 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>

---
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>
---
 xen/arch/x86/mm/p2m.c | 57 ++++++++++++++++++++++++++++++++++++---------------
 1 file changed, 40 insertions(+), 17 deletions(-)

diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
index 80d3331..f3f3764 100644
--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -1043,39 +1043,62 @@ static void change_type_range(struct p2m_domain *p2m,
                               p2m_type_t ot, p2m_type_t nt)
 {
     unsigned long rangeset_start, rangeset_end;
+    unsigned long invalidate_start, invalidate_end;
     struct domain *d = p2m->domain;
     unsigned long host_max_pfn = p2m_get_hostp2m(d)->max_mapped_pfn;
+    unsigned long max_pfn = p2m->max_mapped_pfn;
     int rc = 0;
 
-    rangeset_start = start;
-    rangeset_end   = end - 1;
+    /*
+     * 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.
+     */
+    rangeset_start = invalidate_start = start;
+    rangeset_end   = invalidate_end   = end - 1;
 
-    /* Always clip the rangeset down to the host p2m */
+    /* Clip down to the host p2m */
     if ( unlikely(rangeset_end > host_max_pfn) )
-        rangeset_end = host_max_pfn;
+        rangeset_end = invalidate_end = host_max_pfn;
 
     /* If the requested range is out of scope, return doing nothing */
     if ( rangeset_start > rangeset_end )
         return;
 
+    if ( p2m_is_altp2m(p2m) )
+        invalidate_end = min(invalidate_end, max_pfn);
+
     p2m->defer_nested_flush = 1;
 
     /*
-     * 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 ( !rangeset_start && rangeset_end >= p2m->max_mapped_pfn)
-        p2m->change_entry_type_global(p2m, ot, nt);
-    else
-        rc = p2m->change_entry_type_range(p2m, ot, nt,
-                                          rangeset_start, rangeset_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, rangeset_start, rangeset_end, 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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