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

Cornelia Huck
2020-09-08T08:37:23Z

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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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