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    SubjectRe: [patch 134/149] x86, paravirt: Add a global synchronization point for pvclock
    On 07/14/2010 01:50 PM, H. Peter Anvin wrote:
    > invlpg, in the general case, definitely needs a memory clobber even if
    > volatiles are ordered, since it needs to be ordered with regards to
    > non-volatile memory operations.

    Yes. I'd say write_crX should need that too, since they can they can
    have a variety global effects on how memory addressing works (from tlb
    flush to switching pagetable formats).

    > Note that memory clobbers don't by themselves enforce ordering since
    > they don't prevent the ordering of memory clobbers with respect to each
    > other.

    Hm. Well we do *definitely* rely on that. I guess technically we'd
    need at least a memory input on the asm to be ordered with respect to a
    memory clobber. But that doesn't seem to have been an issue (or perhaps
    its mixed up with the secret semantics of asm volatile).


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