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authorJeremy Fitzhardinge <jeremy@goop.org>2008-03-17 16:36:52 -0700
committerIngo Molnar <mingo@elte.hu>2008-03-27 16:08:45 +0100
commit04c44a080d2f699a3042d4e743f7ad2ffae9d538 (patch)
treef198aa2f653a8b2cd0e4d33ccc68587e9027cd81 /arch/x86/xen/xen-asm.S
parent5abbcf29928966b28d70f8a0da424f55582f8603 (diff)
xen: fix RMW when unmasking events
xen_irq_enable_direct and xen_sysexit were using "andw $0x00ff, XEN_vcpu_info_pending(vcpu)" to unmask events and test for pending ones in one instuction. Unfortunately, the pending flag must be modified with a locked operation since it can be set by another CPU, and the unlocked form of this operation was causing the pending flag to get lost, allowing the processor to return to usermode with pending events and ultimately deadlock. The simple fix would be to make it a locked operation, but that's rather costly and unnecessary. The fix here is to split the mask-clearing and pending-testing into two instructions; the interrupt window between them is of no concern because either way pending or new events will be processed. This should fix lingering bugs in using direct vcpu structure access too. [ Stable: needed in 2.6.24.x ] Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> Cc: Stable <stable@kernel.org> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'arch/x86/xen/xen-asm.S')
-rw-r--r--arch/x86/xen/xen-asm.S9
1 files changed, 7 insertions, 2 deletions
diff --git a/arch/x86/xen/xen-asm.S b/arch/x86/xen/xen-asm.S
index 1a43b60c0c6..6b7190449d0 100644
--- a/arch/x86/xen/xen-asm.S
+++ b/arch/x86/xen/xen-asm.S
@@ -33,12 +33,17 @@
events, then enter the hypervisor to get them handled.
*/
ENTRY(xen_irq_enable_direct)
- /* Clear mask and test pending */
- andw $0x00ff, PER_CPU_VAR(xen_vcpu_info)+XEN_vcpu_info_pending
+ /* Unmask events */
+ movb $0, PER_CPU_VAR(xen_vcpu_info)+XEN_vcpu_info_mask
+
/* Preempt here doesn't matter because that will deal with
any pending interrupts. The pending check may end up being
run on the wrong CPU, but that doesn't hurt. */
+
+ /* Test for pending */
+ testb $0xff, PER_CPU_VAR(xen_vcpu_info)+XEN_vcpu_info_pending
jz 1f
+
2: call check_events
1:
ENDPATCH(xen_irq_enable_direct)