Bhushan Bharat-R65777 [off-list ref] wrote:

quoted

-----Original Message-----
From: Michael Neuling [mailto:mikey@neuling.org]
Sent: Tuesday, February 12, 2013 9:16 AM
To: Bhushan Bharat-R65777
Cc: Wood Scott-B07421; linuxppc-dev@lists.ozlabs.org
Subject: Re: BOOKE KVM calling load_up_fpu from C?

Bhushan Bharat-R65777 [off-list ref] wrote:

quoted

quoted

-----Original Message-----
From: Linuxppc-dev [mailto:linuxppc-dev-
bounces+bharat.bhushan=freescale.com@lists.ozlabs.org] On Behalf Of
bounces+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.

Yes it is SRR1 not MSR.

Yes, SRR1 == the MSR of the user process, not the current MSR.

Also on 32bit it looks like that R9 is assumed to have SRR1.

Yep that too.  

So any idea how it's suppose to work or is it broken?

Mikey