Messages in this thread | | | Subject | Re: [PATCH v1 1/2] s390x: KVM: accept STSI for CPU topology information | From | Pierre Morel <> | Date | Thu, 15 Jul 2021 13:31:55 +0200 |
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On 7/15/21 11:30 AM, Cornelia Huck wrote: > On Thu, Jul 15 2021, David Hildenbrand <david@redhat.com> wrote: > >> On 14.07.21 17:25, 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. >>> >>> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com> >>> --- >>> arch/s390/kvm/priv.c | 11 ++++++++++- >>> 1 file changed, 10 insertions(+), 1 deletion(-) >>> >>> diff --git a/arch/s390/kvm/priv.c b/arch/s390/kvm/priv.c >>> index 9928f785c677..4ab5f8b7780e 100644 >>> --- a/arch/s390/kvm/priv.c >>> +++ b/arch/s390/kvm/priv.c >>> @@ -856,7 +856,7 @@ 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) { >>> kvm_s390_set_psw_cc(vcpu, 3); >>> return 0; >>> } >>> @@ -893,6 +893,15 @@ static int handle_stsi(struct kvm_vcpu *vcpu) >>> goto out_no_data; >>> handle_stsi_3_2_2(vcpu, (void *) mem); >>> break; >>> + case 15: >>> + if (sel1 != 1 || sel2 < 2 || sel2 > 6) >>> + goto out_no_data; >>> + if (vcpu->kvm->arch.user_stsi) { >>> + insert_stsi_usr_data(vcpu, operand2, ar, fc, sel1, sel2); >>> + return -EREMOTE; > > This bypasses the trace event further down. >
Right, I can add a trace. Note that we had no trace in the past.
>>> + } >>> + kvm_s390_set_psw_cc(vcpu, 3); >>> + return 0; >>> } >>> if (kvm_s390_pv_cpu_is_protected(vcpu)) { >>> memcpy((void *)sida_origin(vcpu->arch.sie_block), (void *)mem, >>> >> >> 1. Setting GPRS to 0 >> >> I was wondering why we have the "vcpu->run->s.regs.gprs[0] = 0;" >> for existing fc 1,2,3 in case we set cc=0. >> >> Looking at the doc, all I find is: >> >> "CC 0: Requested configuration-level number placed in >> general register 0 or requested SYSIB informa- >> tion stored" >> >> But I don't find where it states that we are supposed to set >> general register 0 to 0. Wouldn't we also have to do it for >> fc=15 or for none? >> >> If fc 1,2,3 and 15 are to be handled equally, I suggest the following: >> >> diff --git a/arch/s390/kvm/priv.c b/arch/s390/kvm/priv.c >> index 9928f785c677..6eb86fa58b0b 100644 >> --- a/arch/s390/kvm/priv.c >> +++ b/arch/s390/kvm/priv.c >> @@ -893,17 +893,23 @@ static int handle_stsi(struct kvm_vcpu *vcpu) >> goto out_no_data; >> handle_stsi_3_2_2(vcpu, (void *) mem); >> break; >> + case 15: >> + if (sel1 != 1 || sel2 < 2 || sel2 > 6) >> + goto out_no_data; >> + break; >> } >> - if (kvm_s390_pv_cpu_is_protected(vcpu)) { >> - memcpy((void *)sida_origin(vcpu->arch.sie_block), (void *)mem, >> - PAGE_SIZE); >> - rc = 0; >> - } else { >> - rc = write_guest(vcpu, operand2, ar, (void *)mem, PAGE_SIZE); >> - } >> - if (rc) { >> - rc = kvm_s390_inject_prog_cond(vcpu, rc); >> - goto out; >> + if (mem) { >> + if (kvm_s390_pv_cpu_is_protected(vcpu)) { >> + memcpy((void *)sida_origin(vcpu->arch.sie_block), >> + (void *)mem, PAGE_SIZE); >> + } else { >> + rc = write_guest(vcpu, operand2, ar, (void *)mem, >> + PAGE_SIZE); >> + if (rc) { >> + rc = kvm_s390_inject_prog_cond(vcpu, rc); >> + goto out; >> + } >> + } >> } >> if (vcpu->kvm->arch.user_stsi) { >> insert_stsi_usr_data(vcpu, operand2, ar, fc, sel1, sel2); > > Something like that sounds good, the code is getting a bit convoluted. >
OK for me, in that case we can also suppress the check for FC=15 and let that to user space as it was suggested in a previous comment
>> >> >> 2. maximum-MNest facility >> >> " >> 1. If the maximum-MNest facility is installed and >> selector 2 exceeds the nonzero model-depen- >> dent maximum-selector-2 value." >> >> 2. If the maximum-MNest facility is not installed and >> selector 2 is not specified as two. >> " >> >> We will we be handling the presence/absence of the maximum-MNest facility >> (for our guest?) in QEMU, corect? >> >> I do wonder if we should just let any fc=15 go to user space let the whole >> sel1 / sel2 checking be handled there. I don't think it's a fast path after all. >> But no strong opinion. > > If that makes handling easier, I think it would be a good idea.
OK too
> >> >> How do we identify availability of maximum-MNest facility? >> >> >> 3. User space awareness >> >> How can user space identify that we actually forward these intercepts? >> How can it enable them? The old KVM_CAP_S390_USER_STSI capability >> is not sufficient. > > Why do you think that it is not sufficient? USER_STSI basically says > "you may get an exit that tells you about a buffer to fill in some more > data for a stsi command, and we also tell you which call". If userspace > does not know what to add for a certain call, it is free to just do > nothing, and if it does not get some calls it would support, that should > not be a problem, either? > >> >> I do wonder if we want KVM_CAP_S390_USER_STSI_15 or sth like that to change >> the behavior once enabled by user space. >> >> >> 4. Without vcpu->kvm->arch.user_stsi, we indicate cc=0 to our guest, >> also for fc 1,2,3. Is that actually what we want? (or do we simply not care >> because the guest is not supposed to use stsi?) > > If returning an empty buffer is ok, it should not be a problem, I > guess. (I have not looked yet at the actual definitions.) >
When user_stsi is 0 for fc 1,2,3 the buffer is filled in the kernel, for 15 the kernel can not do this.
-- Pierre Morel IBM Lab Boeblingen
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