Re: [Xen-devel] Re: [PATCH] EPT: Flush running cpus, add mask to flush when scheduled in

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

>>> Keir Fraser <keir.fraser@xxxxxxxxxxxxx> 22.09.09 10:07 >>>
>On 22/09/2009 08:07, "Jan Beulich" <JBeulich@xxxxxxxxxx> wrote:
>> Also, merely using cpus_complement() here seem inefficient: It should be
>> possible to accumulate the flush activity, and avoid re-flushing on a CPU
>> which e.g. got flushed on the second from the last run through this code
>> (and not dirtied afterwards). I.e. I'd think there should be cpus_andnot()
>> here, and setting of the bits as CPUs get dirtied.
>
>I don't see how that is possible, as domain_dirty_cpumask can have changed
>arbitrarily since the previous invocation of ept_sync_domain(), as can the
>EPT tables. We have to assume every CPU has potentially stale cached
>mappings.

Why? It ought to be possible to know which CPUs the guest has run on
for any period of time. Any CPU it hasn't run on wouldn't need flushing,
would it?

Jan


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