Messages in this thread | | | Subject | Re: [PATCH] x86/speculation: Update TIF_SPEC_IB before ibpb barrier | From | Zhenzhong Duan <> | Date | Mon, 28 Jan 2019 16:42:41 +0800 |
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On 2019/1/28 16:36, Thomas Gleixner wrote: > On Mon, 28 Jan 2019, Zhenzhong Duan wrote: >> On 2019/1/26 2:03, Thomas Gleixner wrote: >>> Bah, nonsense. Brain was clearly still out for lunch and I confused IBPB >>> and STIBP for a moment. cond_ibpb() is the thing issues in switch_mm() and >>> that is not leaving a stale MSR around because we only write to it when we >>> need the barrier. The bit is not stale because the barrier is only issued >>> with the write. The bit has not to be cleared. >>> >>> So the only 'issue' what happens is that switch_to() either issues a >>> barrier too much or misses one. That's really not a problem. >> >> Ok, yes, the purpose of this patch is to avoid the one missed barrier. > > And that missed barrier is not worth it to do extra work in switch_to/mm > simply because it's a one off event and there is no way to exploit that > reliably.
Got it.
Thanks Zhenzhong
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