From d3a55d7d9bb518efe08143d050deff9f4ee80ec1 Mon Sep 17 00:00:00 2001 From: Andrew Cooper Date: Thu, 4 Jul 2013 10:33:18 +0200 Subject: [PATCH] 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 Acked-by: Keir Fraser --- xen/arch/x86/mm.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c index 77dcafc261..f151dec2b2 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; -- 2.30.2