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

Christian Borntraeger
2020-09-08T09:18:10Z

On 08.09.20 10:36, Cornelia Huck wrote:
> 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 */?

I think we can remove these 2 case statements and rely on the default case anyway.
>
>>
>>>
>>>> + 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:
>>>
>>
>>
>