[Xen-changelog] [xen stable-4.2] x86/mm: Ensure useful progress in alloc_l2_table()

[patchbot@xxxxxxx]

commit 80571b8025d74089dae4314f989b0bb1b2096d47
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Thu Aug 8 10:30:07 2013 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Aug 8 10:30:07 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>
    master commit: d3a55d7d9bb518efe08143d050deff9f4ee80ec1
    master date: 2013-07-04 10:33:18 +0200
---
 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 5b0b953..fcd7939 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -1451,7 +1451,8 @@ 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#stable-4.2

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