Bhushan Bharat-R65777 <r65...@freescale.com> wrote:
>
>
> > -----Original Message-----
> > From: Linuxppc-dev [mailto:linuxppc-dev-
> > bounces+bharat.bhushan=freescale....@lists.ozlabs.org] On Behalf Of Michael
> > Neuling
> > Sent: Tuesday, February 12, 2013 8:59 AM
> > To: Wood Scott-B07421
> > Cc: linuxppc-dev@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@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. It's the MSR of the user process, not the current MSR.
Mikey
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