On 22.01.2026 15:17, Uros Bizjak wrote: > The MCE_GETCLEAR_FLAGS ioctl retrieves xen_mcelog.flags while > atomically clearing it. This was previously implemented using a > cmpxchg() loop. > > Replace the cmpxchg() loop with a single xchg(), which provides the > same atomic get-and-clear semantics, avoids retry spinning under > contention, and simplifies the code. > > The code on x86_64 improves from: > > 186: 8b 15 00 00 00 00 mov 0x0(%rip),%edx > 18c: 89 d0 mov %edx,%eax > 18e: f0 0f b1 0d 00 00 00 lock cmpxchg %ecx,0x0(%rip) > 195: 00 > 196: 39 c2 cmp %eax,%edx > 198: 75 ec jne 186 <...> > > to just: > > 186: 87 05 00 00 00 00 xchg %eax,0x0(%rip) > > No functional change intended. > > Signed-off-by: Uros Bizjak <[email protected]>
Reviewed-by: Jan Beulich <[email protected]>
