From 06fc732c33a7ff5e4c91bcf4a6ca86b5e335ad9a Mon Sep 17 00:00:00 2001 From: Jeremy Fitzhardinge Date: Tue, 3 Feb 2009 16:01:46 -0800 Subject: [PATCH] xen: disable interrupts before saving in percpu Impact: Fix race condition xen_mc_batch has a small preempt race where it takes the address of a percpu variable immediately before disabling interrupts, thereby leaving a small window in which we may migrate to another cpu and save the flags in the wrong percpu variable. Disable interrupts before saving the old flags in a percpu. Signed-off-by: Jeremy Fitzhardinge Signed-off-by: H. Peter Anvin --- arch/x86/xen/multicalls.h | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/arch/x86/xen/multicalls.h b/arch/x86/xen/multicalls.h index 858938241616..fa3e10725d98 100644 --- a/arch/x86/xen/multicalls.h +++ b/arch/x86/xen/multicalls.h @@ -19,8 +19,10 @@ DECLARE_PER_CPU(unsigned long, xen_mc_irq_flags); paired with xen_mc_issue() */ static inline void xen_mc_batch(void) { + unsigned long flags; /* need to disable interrupts until this entry is complete */ - local_irq_save(__get_cpu_var(xen_mc_irq_flags)); + local_irq_save(flags); + __get_cpu_var(xen_mc_irq_flags) = flags; } static inline struct multicall_space xen_mc_entry(size_t args) -- 2.20.1