Re: [PATCH v3 3/3] KVM: s390: vsie: Make use of CRYCB FORMAT2 clear

[Pierre Morel]

On 23/08/2018 13:33, Janosch Frank wrote:
> On 8/23/18 1:21 PM, David Hildenbrand wrote:
> > On 23.08.2018 13:05, Janosch Frank wrote:
> > > On 8/23/18 12:25 PM, Pierre Morel wrote:
> > > > The comment preceding the shadow_crycb function is
> > > > misleading, we effectively accept FORMAT2 CRYCB in the
> > > > guest.
> > >
> > > I beg to differ:
> > >
> > > if (!(crycbd_o & vcpu->arch.sie_block->crycbd & CRYCB_FORMAT1))
> > > 		return 0;
> >
> > FORMAT2 includes bit FORMAT1 (backwards compatible)
>
> Right, this check is very misleading because of the constant, we
> effectively test against Format 0 and Format 2.
>
> Can we make this clearer by explicitly ANDing 0x01 or adding a comment?

yes, done, I modified the comment in front of the function.

> Code makes sense:
> Reviewed-by: Janosch Frank <frankja@xxxxxxxxxxxxx>

Thanks,

regards,
Pierre

> > > > When using FORMAT2 in the host we do not need to or with
> > > > FORMAT1.
> > > >
> > > > Signed-off-by: Pierre Morel <pmorel@xxxxxxxxxxxxx>
> > > > ---
> > > >   arch/s390/kvm/vsie.c | 6 +++---
> > > >   1 file changed, 3 insertions(+), 3 deletions(-)
> > > >
> > > > diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c
> > > > index 38ea5da..e0e6fbf 100644
> > > > --- a/arch/s390/kvm/vsie.c
> > > > +++ b/arch/s390/kvm/vsie.c
> > > > @@ -140,7 +140,8 @@ static int prepare_cpuflags(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
> > > >    * Create a shadow copy of the crycb block and setup key wrapping, if
> > > >    * requested for guest 3 and enabled for guest 2.
> > > >    *
> > > > - * We only accept format-1 (no AP in g2), but convert it into format-2
> > > > + * We accept format-1 or format-2, but we treat it as a format-1 (no AP in g2),
> > > > + * and we convert it into format-2 in the shadow CRYCB.
> > > >    * There is nothing to do for format-0.
> > > >    *
> > > >    * Returns: - 0 if shadowed or nothing to do
> > > > @@ -179,8 +180,7 @@ static int shadow_crycb(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
> > > >   		return set_validity_icpt(scb_s, 0x0035U);
> > > >   
> > > >   	scb_s->ecb3 |= ecb3_flags;
> > > > -	scb_s->crycbd = ((__u32)(__u64) &vsie_page->crycb) | CRYCB_FORMAT1 |
> > > > -			CRYCB_FORMAT2;
> > > > +	scb_s->crycbd = ((__u32)(__u64) &vsie_page->crycb) | CRYCB_FORMAT2;
> > >
> > > That's purely cosmetic but valid.
> > >
> > > >   
> > > >   	/* xor both blocks in one run */
> > > >   	b1 = (unsigned long *) vsie_page->crycb.dea_wrapping_key_mask;
> >
> > Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>


--
Pierre Morel
Linux/KVM/QEMU in BÃblingen - Germany