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

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Fri, 31 Jan 2014 16:58:05 +0530

Paul Mackerras <[email-masked]> writes:

> 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 reason for facility unavailable interrupt is encoded in FSCR right ?

-aneesh