Re: [PATCH v2] KVM: s390: Introduce storage key removal facility

[Cornelia Huck <cohuck@redhat.com>]

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On Tue, 8 Sep 2020 09:52:48 +0200
Janosch Frank <frankja@linux.ibm.com> wrote:

> On 9/7/20 6:30 PM, Cornelia Huck wrote:
> > On Mon,  7 Sep 2020 10:33:52 -0400
> > Janosch Frank <frankja@linux.ibm.com> wrote:
> >   
> >> The storage key removal facility makes skey related instructions
> >> result in special operation program exceptions. It is based on the
> >> Keyless Subset Facility.
> >>
> >> The usual suspects are iske, sske, rrbe and their respective
> >> variants. lpsw(e), pfmf and tprot can also specify a key and essa with
> >> an ORC of 4 will consult the change bit, hence they all result in
> >> exceptions.
> >>
> >> Unfortunately storage keys were so essential to the architecture, that
> >> there is no facility bit that we could deactivate. That's why the
> >> removal facility (bit 169) was introduced which makes it necessary,
> >> that, if active, the skey related facilities 10, 14, 66, 145 and 149
> >> are zero. Managing this requirement and migratability has to be done
> >> in userspace, as KVM does not check the facilities it receives to be
> >> able to easily implement userspace emulation.
> >>
> >> Removing storage key support allows us to circumvent complicated
> >> emulation code and makes huge page support tremendously easier.
> >>
> >> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
> >> ---
> >>
> >> v2:
> >> 	* Removed the likely
> >> 	* Updated and re-shuffeled the comments which had the wrong information
> >>
> >> ---
> >>  arch/s390/kvm/intercept.c | 40 ++++++++++++++++++++++++++++++++++++++-
> >>  arch/s390/kvm/kvm-s390.c  |  5 +++++
> >>  arch/s390/kvm/priv.c      | 26 ++++++++++++++++++++++---
> >>  3 files changed, 67 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/arch/s390/kvm/intercept.c b/arch/s390/kvm/intercept.c
> >> index e7a7c499a73f..983647ea2abe 100644
> >> --- a/arch/s390/kvm/intercept.c
> >> +++ b/arch/s390/kvm/intercept.c
> >> @@ -33,6 +33,7 @@ u8 kvm_s390_get_ilen(struct kvm_vcpu *vcpu)
> >>  	case ICPT_OPEREXC:
> >>  	case ICPT_PARTEXEC:
> >>  	case ICPT_IOINST:
> >> +	case ICPT_KSS:
> >>  		/* instruction only stored for these icptcodes */
> >>  		ilen = insn_length(vcpu->arch.sie_block->ipa >> 8);
> >>  		/* Use the length of the EXECUTE instruction if necessary */
> >> @@ -565,7 +566,44 @@ int kvm_handle_sie_intercept(struct kvm_vcpu *vcpu)
> >>  		rc = handle_partial_execution(vcpu);
> >>  		break;
> >>  	case ICPT_KSS:
> >> -		rc = kvm_s390_skey_check_enable(vcpu);
> >> +		if (!test_kvm_facility(vcpu->kvm, 169)) {
> >> +			rc = kvm_s390_skey_check_enable(vcpu);
> >> +		} else {  
> > 
> > <bikeshed>Introduce a helper function? This is getting a bit hard to
> > read.</bikeshed>
> >   
> >> +			/*
> >> +			 * Storage key removal facility emulation.
> >> +			 *
> >> +			 * KSS is the same priority as an instruction
> >> +			 * interception. Hence we need handling here
> >> +			 * and in the instruction emulation code.
> >> +			 *
> >> +			 * KSS is nullifying (no psw forward), SKRF
> >> +			 * issues suppressing SPECIAL OPS, so we need
> >> +			 * to forward by hand.
> >> +			 */
> >> +			switch (vcpu->arch.sie_block->ipa) {
> >> +			case 0xb2b2:
> >> +				kvm_s390_forward_psw(vcpu, kvm_s390_get_ilen(vcpu));
> >> +				rc = kvm_s390_handle_b2(vcpu);
> >> +				break;
> >> +			case 0x8200:  
> > 
> > Can we have speaking names? I can only guess that this is an lpsw...  
> 
> You can only guess from the kvm_s390_handle_lpsw() call below? ;-)
> 
> I'd be happy to put this into an own function and add some comments to
> the cases where we lack them. However, I don't really want to define
> constants for speaking names.

Well, I can guess the lpsw here :) but not the b2b2 above. Maybe add a
comment like /* handle lpsw/lpswe */?

> 
> >   
> >> +				kvm_s390_forward_psw(vcpu, kvm_s390_get_ilen(vcpu));
> >> +				rc = kvm_s390_handle_lpsw(vcpu);
> >> +				break;
> >> +			case 0:
> >> +				/*
> >> +				 * Interception caused by a key in a
> >> +				 * exception new PSW mask. The guest
> >> +				 * PSW has already been updated to the
> >> +				 * non-valid PSW so we only need to
> >> +				 * inject a PGM.
> >> +				 */
> >> +				rc = kvm_s390_inject_program_int(vcpu, PGM_SPECIFICATION);
> >> +				break;
> >> +			default:
> >> +				kvm_s390_forward_psw(vcpu, kvm_s390_get_ilen(vcpu));
> >> +				rc = kvm_s390_inject_program_int(vcpu, PGM_SPECIAL_OPERATION);
> >> +			}
> >> +		}
> >>  		break;
> >>  	case ICPT_MCHKREQ:
> >>  	case ICPT_INT_ENABLE:  
> >   
> 
> 


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