BOOKE KVM calling load_up_fpu from C?

[Bhushan Bharat-R65777]

> -----Original Message-----
> From: Michael Neuling [mailto:mikey at neuling.org]
> Sent: Tuesday, February 12, 2013 9:16 AM
> To: Bhushan Bharat-R65777
> Cc: Wood Scott-B07421; linuxppc-dev at lists.ozlabs.org
> Subject: Re: BOOKE KVM calling load_up_fpu from C?
> 
> Bhushan Bharat-R65777 <R65777 at freescale.com> wrote:
> 
> >
> >
> > > -----Original Message-----
> > > From: Linuxppc-dev [mailto:linuxppc-dev-
> > > bounces+bharat.bhushan=freescale.com at lists.ozlabs.org] On Behalf Of
> > > bounces+Michael
> > > Neuling
> > > Sent: Tuesday, February 12, 2013 8:59 AM
> > > To: Wood Scott-B07421
> > > Cc: linuxppc-dev at lists.ozlabs.org
> > > Subject: BOOKE KVM calling load_up_fpu from C?
> > >
> > > Scott,
> > >
> > > I was looking at changing how load_up_fpu works and I found this in
> > > arch/powerpc/kvm/booke.h:
> > >
> > > static inline void kvmppc_load_guest_fp(struct kvm_vcpu *vcpu) {
> > > #ifdef CONFIG_PPC_FPU
> > > 	if (vcpu->fpu_active && !(current->thread.regs->msr & MSR_FP)) {
> > > 		load_up_fpu();
> > > 		current->thread.regs->msr |= MSR_FP;
> > > 	}
> > > #endif
> > > }
> > >
> > > I'm wondering how this is suppose to work since load_up_fpu is
> > > suppose to have MSR in R12?
> >
> > Is not the load_up_fpu() does mfmsr:
> >
> > _GLOBAL(load_up_fpu)
> >         mfmsr   r5
> >         ori     r5,r5,MSR_FP
> > #ifdef CONFIG_VSX
> > BEGIN_FTR_SECTION
> >         oris    r5,r5,MSR_VSX at h
> > END_FTR_SECTION_IFSET(CPU_FTR_VSX)
> > #endif
> >         SYNC
> >         MTMSRD(r5)                      /* enable use of fpu now */
> >         isync
> > <snip>
> 
> Look further down...
> 
> #ifdef CONFIG_PPC32
> 	mfspr	r5,SPRN_SPRG_THREAD		/* current task's THREAD (phys) */
> 	lwz	r4,THREAD_FPEXC_MODE(r5)
> 	ori	r9,r9,MSR_FP		/* enable FP for current */
> 	or	r9,r9,r4
> #else
> 	ld	r4,PACACURRENT(r13)
> 	addi	r5,r4,THREAD		/* Get THREAD */
> 	lwz	r4,THREAD_FPEXC_MODE(r5)
> 	ori	r12,r12,MSR_FP
> 	or	r12,r12,r4
> 	std	r12,_MSR(r1)
> #endif
> 
> R12 is loaded with SRR1 in the exception prolog before load_up_fpu is called.

Yes it is SRR1 not MSR.
Also on 32bit it looks like that R9 is assumed to have SRR1.

-Bharat

> It's the MSR of the user process, not the current MSR.
> 
> Mikey