[Xen-changelog] [xen master] x86/p2m: adjust non-PoD accounting in p2m_pod_decrease_reservation()

[patchbot@xxxxxxx]

commit 578f90e3e5e7075e93caeb35625be820e618e856
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Fri Feb 21 17:15:22 2020 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri Feb 21 17:15:22 2020 +0100

    x86/p2m: adjust non-PoD accounting in p2m_pod_decrease_reservation()
    
    Throughout the function the equation
    
            pod + nonpod == (1UL << order)
    
    should hold. This has been violated by the final loop of the function:
    * changing a range from a type other than p2m_populate_on_demand to
      p2m_invalid doesn't alter the amount of non-PoD pages in the region,
    * changing a range from p2m_populate_on_demand to p2m_invalid does
      increase the amount of non-PoD pages in the region along with
      decreasing the amount of PoD pages there.
    Fortunately the variable isn't used anymore after the loop. Instead of
    correcting the updating of the "nonpod" variable, however, drop it
    altogether, to avoid getting the above equation to not hold again by a
    future change.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 xen/arch/x86/mm/p2m-pod.c | 17 +++++------------
 1 file changed, 5 insertions(+), 12 deletions(-)

diff --git a/xen/arch/x86/mm/p2m-pod.c b/xen/arch/x86/mm/p2m-pod.c
index f2c9409568..2a7b8c117b 100644
--- a/xen/arch/x86/mm/p2m-pod.c
+++ b/xen/arch/x86/mm/p2m-pod.c
@@ -509,7 +509,7 @@ p2m_pod_decrease_reservation(struct domain *d, gfn_t gfn, 
unsigned int order)
     unsigned long ret = 0, i, n;
     struct p2m_domain *p2m = p2m_get_hostp2m(d);
     bool_t steal_for_cache;
-    long pod, nonpod, ram;
+    long pod = 0, ram = 0;
 
     gfn_lock(p2m, gfn, order);
     pod_lock(p2m);
@@ -524,8 +524,6 @@ p2m_pod_decrease_reservation(struct domain *d, gfn_t gfn, 
unsigned int order)
     if ( unlikely(d->is_dying) )
         goto out_unlock;
 
-    pod = nonpod = ram = 0;
-
     /* Figure out if we need to steal some freed memory for our cache */
     steal_for_cache =  ( p2m->pod.entry_count > p2m->pod.count );
 
@@ -539,19 +537,15 @@ p2m_pod_decrease_reservation(struct domain *d, gfn_t gfn, 
unsigned int order)
         n = 1UL << min(order, cur_order);
         if ( t == p2m_populate_on_demand )
             pod += n;
-        else
-        {
-            nonpod += n;
-            if ( p2m_is_ram(t) )
-                ram += n;
-        }
+        else if ( p2m_is_ram(t) )
+            ram += n;
     }
 
     /* No populate-on-demand?  Don't need to steal anything?  Then we're 
done!*/
     if ( !pod && !steal_for_cache )
         goto out_unlock;
 
-    if ( !nonpod )
+    if ( i == pod )
     {
         /*
          * All PoD: Mark the whole region invalid and tell caller
@@ -587,7 +581,7 @@ p2m_pod_decrease_reservation(struct domain *d, gfn_t gfn, 
unsigned int order)
          p2m_pod_zero_check_superpage(p2m, _gfn(gfn_x(gfn) & ~(SUPERPAGE_PAGES 
- 1))) )
     {
         pod = 1UL << order;
-        ram = nonpod = 0;
+        ram = 0;
         ASSERT(steal_for_cache == (p2m->pod.entry_count > p2m->pod.count));
     }
 
@@ -655,7 +649,6 @@ p2m_pod_decrease_reservation(struct domain *d, gfn_t gfn, 
unsigned int order)
 
             steal_for_cache =  ( p2m->pod.entry_count > p2m->pod.count );
 
-            nonpod -= n;
             ram -= n;
             ret += n;
         }
--
generated by git-patchbot for /home/xen/git/xen.git#master

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