[Xen-devel] [PATCH V7 4/5] p2m: Always use hostp2m when clipping rangesets

[Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>]

The logdirty rangesets of the altp2ms need to be kept in sync with the
hostp2m.  This means when iterating through the altp2ms, we need to
use the host p2m to clip the rangeset, not the indiviual altp2m's
value.

This change also:

- Documents that the end is non-inclusive

- Calculates an "inclusive" value for the end once, rather than
  open-coding the modification, and (worse) back-modifying updates so
  that the calculation ends up correct

- Clarifies the logic deciding whether to call
  change_entry_type_global() or change_entry_type_range()

- Handles the case where start >= hostp2m->max_mapped_pfn

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>

---
RFC: Wasn't sure what the best thing was to do if start >=
host_max_pfn.  We silently clip the logdirty rangeset to
max_mapped_pfn, and the chosen behavior seems consistent with that.
But it seems like such a request would almost certainly be a bug
somewhere that people might like to find out about.
---
 xen/arch/x86/mm/p2m.c | 44 ++++++++++++++++++++++++++++----------------
 1 file changed, 28 insertions(+), 16 deletions(-)

diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
index 823feb4..80d3331 100644
--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -1037,32 +1037,44 @@ int p2m_change_type_one(struct domain *d, unsigned long 
gfn_l,
     return rc;
 }
 
-/* Modify the p2m type of a range of gfns from ot to nt. */
+/* Modify the p2m type of [start, end) from ot to nt. */
 static void change_type_range(struct p2m_domain *p2m,
                               unsigned long start, unsigned long end,
                               p2m_type_t ot, p2m_type_t nt)
 {
-    unsigned long gfn = start;
+    unsigned long rangeset_start, rangeset_end;
     struct domain *d = p2m->domain;
+    unsigned long host_max_pfn = p2m_get_hostp2m(d)->max_mapped_pfn;
     int rc = 0;
 
+    rangeset_start = start;
+    rangeset_end   = end - 1;
+
+    /* Always clip the rangeset down to the host p2m */
+    if ( unlikely(rangeset_end > host_max_pfn) )
+        rangeset_end = host_max_pfn;
+
+    /* If the requested range is out of scope, return doing nothing */
+    if ( rangeset_start > rangeset_end )
+        return;
+
     p2m->defer_nested_flush = 1;
 
-    if ( unlikely(end > p2m->max_mapped_pfn) )
-    {
-        if ( !gfn )
-        {
-            p2m->change_entry_type_global(p2m, ot, nt);
-            gfn = end;
-        }
-        end = p2m->max_mapped_pfn + 1;
-    }
-    if ( gfn < end )
-        rc = p2m->change_entry_type_range(p2m, ot, nt, gfn, end - 1);
+    /*
+     * If all valid gfns are in the invalidation range, just do a
+     * global type change.  Otherwise, invalidate only the range we
+     * need.
+     */
+    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 )
     {
         printk(XENLOG_G_ERR "Error %d changing Dom%d GFNs [%lx,%lx] from %d to 
%d\n",
-               rc, d->domain_id, start, end - 1, ot, nt);
+               rc, d->domain_id, rangeset_start, rangeset_end, ot, nt);
         domain_crash(d);
     }
 
@@ -1070,11 +1082,11 @@ static void change_type_range(struct p2m_domain *p2m,
     {
     case p2m_ram_rw:
         if ( ot == p2m_ram_logdirty )
-            rc = rangeset_remove_range(p2m->logdirty_ranges, start, end - 1);
+            rc = rangeset_remove_range(p2m->logdirty_ranges, rangeset_start, 
rangeset_end);
         break;
     case p2m_ram_logdirty:
         if ( ot == p2m_ram_rw )
-            rc = rangeset_add_range(p2m->logdirty_ranges, start, end - 1);
+            rc = rangeset_add_range(p2m->logdirty_ranges, rangeset_start, 
rangeset_end);
         break;
     default:
         break;
-- 
2.7.4


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