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    SubjectRe: [QUERY] lguest64
    On Fri, Aug 02, 2013 at 03:09:34PM -0400, Konrad Rzeszutek Wilk wrote:
    > On Wed, Jul 31, 2013 at 06:25:04AM -0700, H. Peter Anvin wrote:
    > > On 07/31/2013 06:17 AM, Konrad Rzeszutek Wilk wrote:
    > > >>
    > > >> The big problem with pvops is that they are a permanent tax on future
    > > >> development -- a classic case of "the hooks problem." As such it is
    > > >> important that there be a real, significant, use case with enough users
    > > >> to make the pain worthwhile. With Xen looking at sunsetting PV support
    > > >> with a long horizon, it might currently be possible to remove pvops some
    > > >
    > > > PV MMU parts specifically.
    > > >
    > >
    > > Pretty much stuff that is driverized on plain hardware doesn't matter.
    > > What are you looking at with respect to the basic CPU control state?
    >
    >
    > CC-ing Mukesh here.
    >
    > Let me iterate down what the experimental patch uses:
    >
    > struct pv_init_ops pv_init_ops;
    > [still use xen_patch, but I think that is not needed anymore]
    >
    > struct pv_time_ops pv_time_ops;
    > [we need that as we are using the PV clock source]
    >
    > struct pv_cpu_ops pv_cpu_ops;
    > [only end up using cpuid. This one is a tricky one. We could
    > arguable remove it but it does do some filtering - for example
    > THERM is turned off, or MWAIT if a certain hypercall tells us to
    > disable that. Since this is now a trapped operation this could be
    > handled in the hypervisor - but then it would be in charge of
    > filtering certain CPUID - and this is at bootup - so there is not
    > user interaction. This needs a bit more of thinking]
    >
    read_msr/write_msr in this one make all msr accesses safe. IIRC there
    are MSRs that Linux uses without checking cpuid bits.
    IA32_PERF_CAPABILITIES for instance is used without checking PDCM bit.


    --
    Gleb.


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