Messages in this thread | | | Subject | Re: [PATCH v3 1/3] s390x: KVM: accept STSI for CPU topology information | From | Pierre Morel <> | Date | Wed, 1 Sep 2021 11:43:00 +0200 |
| |
On 8/31/21 3:59 PM, David Hildenbrand wrote: > On 03.08.21 10:26, Pierre Morel wrote: >> STSI(15.1.x) gives information on the CPU configuration topology. >> Let's accept the interception of STSI with the function code 15 and >> let the userland part of the hypervisor handle it when userland >> support the CPU Topology facility. >> >> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com> >> --- >> arch/s390/kvm/priv.c | 7 ++++++- >> 1 file changed, 6 insertions(+), 1 deletion(-) >> >> diff --git a/arch/s390/kvm/priv.c b/arch/s390/kvm/priv.c >> index 9928f785c677..8581b6881212 100644 >> --- a/arch/s390/kvm/priv.c >> +++ b/arch/s390/kvm/priv.c >> @@ -856,7 +856,8 @@ static int handle_stsi(struct kvm_vcpu *vcpu) >> if (vcpu->arch.sie_block->gpsw.mask & PSW_MASK_PSTATE) >> return kvm_s390_inject_program_int(vcpu, PGM_PRIVILEGED_OP); >> - if (fc > 3) { >> + if ((fc > 3 && fc != 15) || >> + (fc == 15 && !test_kvm_facility(vcpu->kvm, 11))) { >> kvm_s390_set_psw_cc(vcpu, 3); >> return 0; >> } >> @@ -893,6 +894,10 @@ static int handle_stsi(struct kvm_vcpu *vcpu) >> goto out_no_data; >> handle_stsi_3_2_2(vcpu, (void *) mem); >> break; >> + case 15: >> + trace_kvm_s390_handle_stsi(vcpu, fc, sel1, sel2, operand2); >> + insert_stsi_usr_data(vcpu, operand2, ar, fc, sel1, sel2); >> + return -EREMOTE; >> } >> if (kvm_s390_pv_cpu_is_protected(vcpu)) { >> memcpy((void *)sida_origin(vcpu->arch.sie_block), (void *)mem, >> > > Sorry, I'm a bit rusty on s390x kvm facility handling. > > > For test_kvm_facility() to succeed, the facility has to be in both: > > a) fac_mask: actually available on the HW and supported by KVM > (kvm_s390_fac_base via FACILITIES_KVM, kvm_s390_fac_ext via > FACILITIES_KVM_CPUMODEL) > > b) fac_list: enabled for a VM > > AFAIU, facility 11 is neither in FACILITIES_KVM nor > FACILITIES_KVM_CPUMODEL, and I remember it's a hypervisor-managed bit. > > So unless we unlock facility 11 in FACILITIES_KVM_CPUMODEL, will > test_kvm_facility(vcpu->kvm, 11) ever successfully trigger here? > > > I'm pretty sure I am messing something up :) >
I think it is the same remark that Christian did as wanted me to use the arch/s390/tools/gen_facilities.c to activate the facility.
The point is that CONFIGURATION_TOPOLOGY, STFL, 11, is already defined inside QEMU since full_GEN10_GA1, so the test_kvm_facility() will succeed with the next patch setting the facility 11 in the mask when getting the KVM_CAP_S390_CPU_TOPOLOGY from userland.
But if we activate it in KVM via any of the FACILITIES_KVM_xxx in the gen_facilities.c we will activate it for the guest what ever userland hypervizor we have, including old QEMU which will generate an exception.
In this circumstances we have the choice between:
- use FACILITY_KVM and handle everything in kernel - use FACILITY_KVM and use an extra CAPABILITY to handle part in kernel to avoid guest crash and part in userland - use only the extra CAPABILITY and handle almost everything in userland
I want to avoid kernel code when not really necessary so I eliminated the first option.
The last two are not very different but I found a better integration using the last one, allowing to use standard test_[kvm_]facility()
Thanks for reviewing.
Regards, Pierre
-- Pierre Morel IBM Lab Boeblingen
| |