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Commit 06fc732c authored by Jeremy Fitzhardinge's avatar Jeremy Fitzhardinge Committed by H. Peter Anvin
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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: default avatarJeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: default avatarH. Peter Anvin <hpa@zytor.com>
parent b1792e36

arch/x86/xen/multicalls.h

+3 −1
Original line number Original line Diff line number Diff line
@@ -19,8 +19,10 @@ DECLARE_PER_CPU(unsigned long, xen_mc_irq_flags); 
   paired with xen_mc_issue() */

   paired with xen_mc_issue() */

static inline void xen_mc_batch(void)

static inline void xen_mc_batch(void)

{

{

	unsigned long flags;

	/* need to disable interrupts until this entry is complete */

	/* 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)

static inline struct multicall_space xen_mc_entry(size_t args)