Re: [PATCH 2/3] KVM: PPC: Book3S HV: Implement virtual mode H_PAGE_INIT handler

[Suraj Jitindar Singh <sjitindarsingh@gmail.com>]

On Tue, 2019-03-19 at 17:53 +1100, Alexey Kardashevskiy wrote:
> 
> On 19/03/2019 15:04, Suraj Jitindar Singh wrote:
> > Implement a virtual mode handler for the H_CALL H_PAGE_INIT which
> > can be
> > used to zero or copy a guest page. The page is defined to be 4k and
> > must
> > be 4k aligned.
> > 
> > The in-kernel handler halves the time to handle this H_CALL
> > compared to
> > handling it in userspace for a radix guest.
> > 
> > Signed-off-by: Suraj Jitindar Singh <sjitindarsingh@gmail.com>
> > ---
> >  arch/powerpc/kvm/book3s_hv.c | 39
> > +++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 39 insertions(+)
> > 
> > diff --git a/arch/powerpc/kvm/book3s_hv.c
> > b/arch/powerpc/kvm/book3s_hv.c
> > index 7179ea783f4f..fa29cc4900c2 100644
> > --- a/arch/powerpc/kvm/book3s_hv.c
> > +++ b/arch/powerpc/kvm/book3s_hv.c
> > @@ -883,6 +883,39 @@ static int kvmppc_copy_guest(struct kvm *kvm,
> > gpa_t to, gpa_t from,
> >  	return 0;
> >  }
> >  
> > +static int kvmppc_h_page_init(struct kvm_vcpu *vcpu, unsigned long
> > flags,
> 
> 
> 
> > +			      unsigned long dest, unsigned long
> > src)
> > +{
> > +	int ret = H_FUNCTION;
> > +	u64 pg_sz = 1UL << 12;	/* 4K page size */
> > +	u64 pg_mask = pg_sz - 1;
> 
> 
> Ditch pg_sz and just use SZ_4K? The page size is not going to change
> here ever.

Yep, will do. Didn't realise that was a thing

> 
> 
> > +
> > +	/* Check for invalid flags (H_PAGE_SET_LOANED covers all
> > CMO flags) */
> > +	if (flags & ~(H_ICACHE_INVALIDATE | H_ICACHE_SYNCHRONIZE |
> > +		      H_ZERO_PAGE | H_COPY_PAGE |
> > H_PAGE_SET_LOANED))
> > +		return H_PARAMETER;
> > +
> > +	/* dest (and src if copy_page flag set) must be page
> > aligned */
> > +	if ((dest & pg_mask) || ((flags & H_COPY_PAGE) && (src &
> > pg_mask)))
> > +		return H_PARAMETER;
> > +
> > +	/* zero and/or copy the page as determined by the flags */
> > +	if (flags & H_ZERO_PAGE) {
> > +		ret = kvm_clear_guest(vcpu->kvm, dest, pg_sz);
> > +		if (ret < 0)
> > +			return H_PARAMETER;
> > +	}
> > +	if (flags & H_COPY_PAGE) {
> 
> 
> If H_COPY_PAGE is set, is there any good reason to do kvm_clear_guest
> first even if H_ZERO_PAGE is set? It should not happen in practice
> and
> it is no harm but also no sense.

True, if both are set then we can get away with only doing copy since
it will have the same effect.

> 
> > +		ret = kvmppc_copy_guest(vcpu->kvm, dest, src,
> > pg_sz);
> > +		if (ret < 0)
> > +			return H_PARAMETER;
> > +	}
> 
> 
> else if (src)
> 	return H_PARAMETER;

I'm not sure that's technically an error so I'm going to leave it out.

> 
> 
> 
> > +
> > +	/* We can ignore the remaining flags */
> > +
> > +	return H_SUCCESS;
> > +}
> > +
> >  static int kvm_arch_vcpu_yield_to(struct kvm_vcpu *target)
> >  {
> >  	struct kvmppc_vcore *vcore = target->arch.vcore;
> > @@ -1083,6 +1116,11 @@ int kvmppc_pseries_do_hcall(struct kvm_vcpu
> > *vcpu)
> >  		if (nesting_enabled(vcpu->kvm))
> >  			ret > > kvmhv_copy_tofrom_guest_nested(vcpu);
> >  		break;
> > +	case H_PAGE_INIT:
> > +		ret = kvmppc_h_page_init(vcpu,
> > kvmppc_get_gpr(vcpu, 4),
> > +					 kvmppc_get_gpr(vcpu, 5),
> > +					 kvmppc_get_gpr(vcpu, 6));
> > +		break;
> >  	default:
> >  		return RESUME_HOST;
> >  	}
> > @@ -1127,6 +1165,7 @@ static int kvmppc_hcall_impl_hv(unsigned long
> > cmd)
> >  	case H_IPOLL:
> >  	case H_XIRR_X:
> >  #endif
> > +	case H_PAGE_INIT:
> >  		return 1;
> >  	}
> >  
> > 
> 
>