[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] Re: [GIT PULL] xen /proc/mtrr implementation
>>> Ingo Molnar <mingo@xxxxxxx> 19.05.09 11:59 >>> >Exactly what is 'bizarre' about using the API defined by the _CPU_ >already, without adding any ad-hoc hypecall? Catch the dom0 WRMSRs, >filter out the MTRR indices - that's it. But that is *not* the same as using the hypercalls: The hypercall tells Xen "Change all CPUs' MTRRs with the indicated index to the indicated value", while the MSR write says "Change the MTRR with the given index on the physical CPU the current virtual CPU happens to run on to the given value". A write-base/write-mask pair may happen to get interrupted (preempted) by the hypervisor, and hence the two writes may happen on different pCPU-s. Teaching the hypervisor to (correctly!) guess what the guest meant in that situation isn't trivial, as then it needs to handle all possible situations (and it can never know whether Dom0 really intended to do something that may look bogus/inconsistent at the first glance). This is even more so considering that Linux is not the only OS capable of running as Dom0. An apparently relatively simple solution - latch the writes and commit them only when the global view became consistent again - isn't possible, since Dom0 may not have a vCPU running on each individual pCPU. Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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