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| author | Jeremy Fitzhardinge <jeremy@goop.org> | 2008-03-17 16:36:52 -0700 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2008-03-27 16:08:45 +0100 |
| commit | 04c44a080d2f699a3042d4e743f7ad2ffae9d538 (patch) | |
| tree | f198aa2f653a8b2cd0e4d33ccc68587e9027cd81 | |
| parent | 5abbcf29928966b28d70f8a0da424f55582f8603 (diff) | |
| download | linux-04c44a080d2f699a3042d4e743f7ad2ffae9d538.tar.gz | |
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>
| -rw-r--r-- | arch/x86/xen/enlighten.c | 2 | ||||
| -rw-r--r-- | arch/x86/xen/xen-asm.S | 9 |
2 files changed, 8 insertions, 3 deletions
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c index 8b9ee27805fd..1a20318c8cff 100644 --- a/arch/x86/xen/enlighten.c +++ b/arch/x86/xen/enlighten.c @@ -95,7 +95,7 @@ struct shared_info *HYPERVISOR_shared_info = (void *)&dummy_shared_info; * * 0: not available, 1: available */ -static int have_vcpu_info_placement = 0; +static int have_vcpu_info_placement = 1; static void __init xen_vcpu_setup(int cpu) { 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) |