| Date | Fri, 27 Apr 2007 00:08:07 -0700 | From | Jeremy Fitzhardinge <> | Subject | Re: [PATCH 06/25] xen: Core Xen implementation |
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Andi Kleen wrote: >> + /* convert from IF type flag */ >> + flags = !(flags & X86_EFLAGS_IF); >> + vcpu = x86_read_percpu(xen_vcpu); >> + vcpu->evtchn_upcall_mask = flags; >> + if (flags == 0) { >> + barrier(); /* unmask then check (avoid races) */ >> > > Don't you need a rmb() here then? The CPU could speculate reads > (more occurrences) >
Is rmb() sufficient? It will stop a speculative read on the pending flag, but will it make sure the write has happened by then? Ie, is it a write-vs-read barrier, or just a read-vs-read? Documentation/memory-barriers.txt suggests not.
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