Re: [PATCH 24/26] KVM: PPC: PV mtmsrd L=0 and mtmsr

Segher Boessenkool
2010-06-29T07:37:39Z

>>> There is also a form of mtmsr where all bits need to be
>>> addressed. While the
>>> PPC64 Linux kernel behaves resonably well here, the PPC32 one
>>> never uses the
>>> L=1 form but does mtmsr even for simple things like only changing
>>> EE.
>>
>> You make it sound like the 32-bit kernel does something stupid, while
>> there is no other choice. The "L=1" thing only exists for 64-bit.
>
> Oh, so that's why :). That doesn't really change the fact that it's
> very hard to distinguish between a mtmsr that only changes MSR_EE
> vs one that changes MSR_IR for example :).

Hard to predict for the CPU as well, guess why there is a separate
instruction now :-P

By the way, L=1 _does_ exist for mtmsr; it's just that no 32-bit
"classic"
implementations support it.

Segher