[PATCH V10 4/5] p2m: Always use hostp2m when clipping rangesets

[Razvan Cojocaru <rcojocaru@bitdefender.com>]

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@citrix.com>
Signed-off-by: Razvan Cojocaru <rcojocaru@bitdefender.com>

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

---
Changes since V9:
 - Removed the patch RFC (replaced by a printk(XENLOG_G_WARNING).
 - Reused start and end in change_type_range() and removed the
   intermediary variables range_start and range_end.
 - Added an extra explanation for the if ( start > end ) return;
   code in the comment.
 - Changed ""Error %d changing Dom%d GFNs [%lx,%lx]" to
   "Error %d changing Dom%d GFNs [%lx,%lx)".
---
 xen/arch/x86/mm/p2m.c | 51 ++++++++++++++++++++++++++++++++++-----------------
 1 file changed, 34 insertions(+), 17 deletions(-)

diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
index d145850..fde2012 100644
--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -1002,30 +1002,47 @@ 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;
     struct domain *d = p2m->domain;
+    const unsigned long host_max_pfn = p2m_get_hostp2m(d)->max_mapped_pfn;
     int rc = 0;
 
-    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);
+    --end;
+
+    if ( start >= host_max_pfn )
+        printk(XENLOG_G_WARNING "Dom%d logdirty rangeset clipped to max_mapped_pfn\n",
+               d->domain_id);
+
+    /* Always clip the rangeset down to the host p2m */
+    if ( unlikely(end > host_max_pfn) )
+        end = host_max_pfn;
+
+    /*
+     * If the requested range is out of scope, return doing nothing.
+     * Attempting to continue will crash the hypervisor in rangeset_add_range()
+     * which ASSERT()s that start <= end.
+     */
+    if ( start > end )
+        return;
+
+    /*
+     * If all valid gfns are in the invalidation range, just do a
+     * global type change. Otherwise, invalidate only the range we
+     * need.
+     */
+    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 )
     {
-        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);
+        printk(XENLOG_G_ERR "Error %d changing Dom%d GFNs [%lx,%lx) from %d to %d\n",
+               rc, d->domain_id, start, end, ot, nt);
         domain_crash(d);
     }
 
@@ -1033,11 +1050,11 @@ 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, start, 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, start, end);
         break;
     default:
         break;
-- 
2.7.4


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