Re: [PATCH] KVM: PPC: Book3S HV: Check for updated HDSISR on P9 HDSI exception

[David Gibson <david@gibson.dropbear.id.au>]

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On Fri, Sep 22, 2017 at 10:46:36AM +0200, Paolo Bonzini wrote:
> On 15/09/2017 07:26, Michael Neuling wrote:
> > On POWER9 DD2.1 and below, sometimes on a Hypervisor Data Storage
> > Interrupt (HDSI) the HDSISR is not be updated at all.
> > 
> > To work around this we put a canary value into the HDSISR before
> > returning to a guest and then check for this canary when we take a
> > HDSI. If we find the canary on a HDSI, we know the hardware didn't
> > update the HDSISR. In this case we return to the guest to retake the
> > HDSI which should correctly update the HDSISR the second time HDSI
> > entry.
> > 
> > After talking to Paulus we've applied this workaround to all POWER9
> > CPUs. The workaround of returning to the guest shouldn't ever be
> > triggered on well behaving CPU. The extra instructions should have
> > negligible performance impact.
> > 
> > Signed-off-by: Michael Neuling <mikey@neuling.org>
> > ---
> >  arch/powerpc/kvm/book3s_hv_rmhandlers.S | 14 +++++++++++++-
> >  1 file changed, 13 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
> > index 663a4a861e..70dca60569 100644
> > --- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
> > +++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
> > @@ -1118,6 +1118,13 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
> >  BEGIN_FTR_SECTION
> >  	mtspr	SPRN_PPR, r0
> >  END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
> > +
> > +/* Move canary into DSISR to check for later */
> > +BEGIN_FTR_SECTION
> > +	li	r0, 0x7fff
> > +	mtspr	SPRN_HDSISR, r0
> > +END_FTR_SECTION_IFSET(CPU_FTR_ARCH_300)
> > +
> >  	ld	r0, VCPU_GPR(R0)(r4)
> >  	ld	r4, VCPU_GPR(R4)(r4)
> >  
> > @@ -1947,9 +1954,14 @@ END_MMU_FTR_SECTION_IFSET(MMU_FTR_TYPE_RADIX)
> >  kvmppc_hdsi:
> >  	ld	r3, VCPU_KVM(r9)
> >  	lbz	r0, KVM_RADIX(r3)
> > -	cmpwi	r0, 0
> >  	mfspr	r4, SPRN_HDAR
> >  	mfspr	r6, SPRN_HDSISR
> > +BEGIN_FTR_SECTION
> > +	/* Look for DSISR canary. If we find it, retry instruction */
> > +	cmpdi	r6, 0x7fff
> > +	beq	6f
> > +END_FTR_SECTION_IFSET(CPU_FTR_ARCH_300)
> > +	cmpwi	r0, 0
> >  	bne	.Lradix_hdsi		/* on radix, just save DAR/DSISR/ASDR */
> >  	/* HPTE not found fault or protection fault? */
> >  	andis.	r0, r6, (DSISR_NOHPTE | DSISR_PROTFAULT)@h
> > 
> 
> Applied to kvm/master, thanks.

I'm not seeing it; have you pushed out the tree?

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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