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SubjectRe: [GIT PULL] xen /proc/mtrr implementation
Ingo Molnar wrote:
>> That's it. I could add any number of bizarre convolutions to
>> achieve the same effect, but given that there's an existing
>> interface that is exactly designed for what we want to achieve, I
>> have to admit it didn't occur to me to do anything else.
>>
>
> 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.
>

Well, the x86 world can't seem to decide what the ABI is supposed to be,
which is why we have mtrr_ops in the first place. Doing emulation at
the MSR level means that I'd need to decide which MTRR interface we're
emulating today and do that.

Yes, I realize that almost everyone is using the same Intel-like
interface these days, but it does mean there's a level of fragility that
doesn't exist if we just implement mtrr_ops.

There's some secondary issues which arise. For example, the mtrr
trimming test is meaningless in dom0 (the e820 is fake, so it doesn't
make sense to compare it with the mtrrs); we currently avoid that
because the test only happens if the mtrr vendor is Intel. We would
need to disable that test some other way.

J


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