[RFC PATCH 07/10] KVM: PPC: BOOK3S: PR: Emulate facility status and control register

Alexander Graf agraf at suse.de
Thu Jan 30 21:02:05 EST 2014

> Am 30.01.2014 um 07:00 schrieb Paul Mackerras <paulus at samba.org>:
>> On Tue, Jan 28, 2014 at 10:14:12PM +0530, Aneesh Kumar K.V wrote:
>> We allow priv-mode update of this. The guest value is saved in fscr,
>> and the value actually used is saved in shadow_fscr. shadow_fscr
>> only contains values that are allowed by the host. On
>> facility unavailable interrupt, if the facility is allowed by fscr
>> but disabled in shadow_fscr we need to emulate the support. Currently
>> all but EBB is disabled. We still don't support performance monitoring
>> in PR guest.
> ...
>> +    /*
>> +     * Save the current fscr in shadow fscr
>> +     */
>> +    mfspr r3,SPRN_FSCR
>> +    PPC_STL r3, VCPU_SHADOW_FSCR(r7)
> I don't think you need to do this.  What could possibly have changed
> FSCR since we loaded it on the way into the guest?

The interrupt cause is part of fscr. But yes, we only meed to store that on an fscr interrupt.

Do we use anything from fscr inside the kernel? Could we switch it lazily on vcpu_load/put?


> Paul.

More information about the Linuxppc-dev mailing list