Diffstat (limited to 'arch/x86/include/asm/bitops.h')
1 files changed, 7 insertions, 0 deletions
diff --git a/arch/x86/include/asm/bitops.h b/arch/x86/include/asm/bitops.h
index a6983b27722..72f5009deb5 100644
@@ -264,6 +264,13 @@ static inline int test_and_clear_bit(int nr, volatile unsigned long *addr)
* This operation is non-atomic and can be reordered.
* If two examples of this operation race, one can appear to succeed
* but actually fail. You must protect multiple accesses with a lock.
+ * Note: the operation is performed atomically with respect to
+ * the local CPU, but not other CPUs. Portable code should not
+ * rely on this behaviour.
+ * KVM relies on this behaviour on x86 for modifying memory that is also
+ * accessed from a hypervisor on the same CPU if running in a VM: don't change
+ * this without also updating arch/x86/kernel/kvm.c
static inline int __test_and_clear_bit(int nr, volatile unsigned long *addr)