From 04c44a080d2f699a3042d4e743f7ad2ffae9d538 Mon Sep 17 00:00:00 2001 From: Jeremy Fitzhardinge Date: Mon, 17 Mar 2008 16:36:52 -0700 Subject: 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 Cc: Stable Signed-off-by: Ingo Molnar --- arch/x86/xen/xen-asm.S | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) (limited to 'arch/x86/xen/xen-asm.S') diff --git a/arch/x86/xen/xen-asm.S b/arch/x86/xen/xen-asm.S index 1a43b60c0c62..6b7190449d07 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) -- cgit v1.2.3