[Xen-changelog] [xen master] x86/mm: Ensure useful progress in alloc_l2_table()

[patchbot@xxxxxxx]

commit d3a55d7d9bb518efe08143d050deff9f4ee80ec1
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Thu Jul 4 10:33:18 2013 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Jul 4 10:33:18 2013 +0200

    x86/mm: Ensure useful progress in alloc_l2_table()
    
    While debugging the issue which turned out to be XSA-58, a printk in this 
loop
    showed that it was quite easy to never make useful progress, because of
    consistently failing the preemption check.
    
    One single l2 entry is a reasonable amount of work to do, even if an action 
is
    pending, and also assures forwards progress across repeat continuations.
    
    Tweak the continuation criteria to fail on the first iteration of the loop.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Acked-by: Keir Fraser <keir@xxxxxxx>
---
 xen/arch/x86/mm.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index 77dcafc..f151dec 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -1278,7 +1278,8 @@ static int alloc_l2_table(struct page_info *page, 
unsigned long type,
 
     for ( i = page->nr_validated_ptes; i < L2_PAGETABLE_ENTRIES; i++ )
     {
-        if ( preemptible && i && hypercall_preempt_check() )
+        if ( preemptible && i > page->nr_validated_ptes
+             && hypercall_preempt_check() )
         {
             page->nr_validated_ptes = i;
             rc = -EAGAIN;
--
generated by git-patchbot for /home/xen/git/xen.git#master

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