Jan Beulich
2009-Apr-20 11:29 UTC
[Xen-devel] [PATCH] x86: fix next->vcpu_dirty_cpumask checking in context_switch()
There was a timing window where flush_tlb_mask() could be called with an empty mask (triggering a WARN_ON() in send_IPI_mask_flat() along with APIC errors) because rather than using the already taken snapshot of next''s vcpu_dirty_cpumask struct vcpu''s field was used directly, which can get its only bit cleared by remote CPUs. Replacing the structure field''s use by the local variable then made the inner cpus_empty() check completely redundant with the one in the surrounding if()''s condition. Signed-off-by: Jan Beulich <jbeulich@novell.com> --- 2009-03-27.orig/xen/arch/x86/domain.c 2009-04-20 13:00:16.000000000 +0200 +++ 2009-03-27/xen/arch/x86/domain.c 2009-04-20 13:03:34.000000000 +0200 @@ -1325,8 +1325,7 @@ void context_switch(struct vcpu *prev, s if ( unlikely(!cpu_isset(cpu, dirty_mask) && !cpus_empty(dirty_mask)) ) { /* Other cpus call __sync_lazy_execstate from flush ipi handler. */ - if ( !cpus_empty(next->vcpu_dirty_cpumask) ) - flush_tlb_mask(next->vcpu_dirty_cpumask); + flush_tlb_mask(dirty_mask); } if ( is_hvm_vcpu(prev) && !list_empty(&prev->arch.hvm_vcpu.tm_list) ) _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel