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SubjectRe: [PATCH v10 2/3] KVM: s390: guest support for topology function
On 6/20/22 14:54, Pierre Morel wrote:
> We report a topology change to the guest for any CPU hotplug.
>
> The reporting to the guest is done using the Multiprocessor
> Topology-Change-Report (MTCR) bit of the utility entry in the guest's
> SCA which will be cleared during the interpretation of PTF.
>
> On every vCPU creation we set the MCTR bit to let the guest know the
> next time he uses the PTF with command 2 instruction that the
> topology changed and that he should use the STSI(15.1.x) instruction
> to get the topology details.
>
> 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/include/asm/kvm_host.h | 11 ++++++++---
> arch/s390/kvm/kvm-s390.c | 27 ++++++++++++++++++++++++++-
> arch/s390/kvm/priv.c | 15 +++++++++++----
> arch/s390/kvm/vsie.c | 3 +++
> 4 files changed, 48 insertions(+), 8 deletions(-)
>
> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
> index 766028d54a3e..bb54196d4ed6 100644
> --- a/arch/s390/include/asm/kvm_host.h
> +++ b/arch/s390/include/asm/kvm_host.h
> @@ -97,15 +97,19 @@ struct bsca_block {
> union ipte_control ipte_control;
> __u64 reserved[5];
> __u64 mcn;
> - __u64 reserved2;
> +#define SCA_UTILITY_MTCR 0x8000

I'm not too happy having this in the bsca but not in the esca. I'd
suggest putting it outside the structs or to go with my next suggestion:

Just make it a bit field struct and make that a member in bsca/esca.
No messing about with ANDing, ORing etc.

It's unfortunate that we only use one bit in that field but I'd still
find it easier to read.

> + __u16 utility;
> + __u8 reserved2[6];
> struct bsca_entry cpu[KVM_S390_BSCA_CPU_SLOTS];
> };
>
> struct esca_block {
> union ipte_control ipte_control;
> - __u64 reserved1[7];
> + __u64 reserved1[6];
> + __u16 utility;
> + __u8 reserved2[6];
> __u64 mcn[4];
> - __u64 reserved2[20];
> + __u64 reserved3[20];
> struct esca_entry cpu[KVM_S390_ESCA_CPU_SLOTS];
> };
>
> @@ -249,6 +253,7 @@ struct kvm_s390_sie_block {
> #define ECB_SPECI 0x08
> #define ECB_SRSI 0x04
> #define ECB_HOSTPROTINT 0x02
> +#define ECB_PTF 0x01
> __u8 ecb; /* 0x0061 */
> #define ECB2_CMMA 0x80
> #define ECB2_IEP 0x20
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index 8fcb56141689..95b96019ca8e 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -1691,6 +1691,25 @@ static int kvm_s390_get_cpu_model(struct kvm *kvm, struct kvm_device_attr *attr)
> return ret;
> }
>
> +/**
> + * kvm_s390_sca_set_mtcr
> + * @kvm: guest KVM description
> + *
> + * Is only relevant if the topology facility is present,
> + * the caller should check KVM facility 11

I'm not sure that this statement make sense since you set the mctr in
kvm_s390_vcpu_setup() unconditionally and don't check stfle 11.

I think we can remove the second line from this.

> + *
> + * Updates the Multiprocessor Topology-Change-Report to signal
> + * the guest with a topology change.

Please swap those two comments

> + */
> +static void kvm_s390_sca_set_mtcr(struct kvm *kvm)
> +{
> + struct bsca_block *sca = kvm->arch.sca; /* SCA version doesn't matter */

Please put the comment above the statement and maybe extend it a bit:
SCA version doesn't matter, the utility field always has the same offset.

> +
> + ipte_lock(kvm);
> + sca->utility |= SCA_UTILITY_MTCR;
> + ipte_unlock(kvm);
> +}
> +
> static int kvm_s390_vm_set_attr(struct kvm *kvm, struct kvm_device_attr *attr)
> {
> int ret;
> @@ -3143,7 +3162,6 @@ __u64 kvm_s390_get_cpu_timer(struct kvm_vcpu *vcpu)
>
> void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
> {
> -

Please remove that change

> gmap_enable(vcpu->arch.enabled_gmap);
> kvm_s390_set_cpuflags(vcpu, CPUSTAT_RUNNING);
> if (vcpu->arch.cputm_enabled && !is_vcpu_idle(vcpu))
> @@ -3272,6 +3290,11 @@ static int kvm_s390_vcpu_setup(struct kvm_vcpu *vcpu)
> vcpu->arch.sie_block->ecb |= ECB_HOSTPROTINT;
> if (test_kvm_facility(vcpu->kvm, 9))
> vcpu->arch.sie_block->ecb |= ECB_SRSI;
> +
> + /* PTF needs guest facilities to enable interpretation */
> + if (test_kvm_facility(vcpu->kvm, 11))
> + vcpu->arch.sie_block->ecb |= ECB_PTF;
> +
> if (test_kvm_facility(vcpu->kvm, 73))
> vcpu->arch.sie_block->ecb |= ECB_TE;
> if (!kvm_is_ucontrol(vcpu->kvm))
> @@ -3403,6 +3426,8 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
> rc = kvm_s390_vcpu_setup(vcpu);
> if (rc)
> goto out_ucontrol_uninit;
> +
> + kvm_s390_sca_set_mtcr(vcpu->kvm);
> return 0;
>
> out_ucontrol_uninit:
> diff --git a/arch/s390/kvm/priv.c b/arch/s390/kvm/priv.c
> index 12c464c7cddf..77a692238585 100644
> --- a/arch/s390/kvm/priv.c
> +++ b/arch/s390/kvm/priv.c
> @@ -873,10 +873,13 @@ 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) {
> - kvm_s390_set_psw_cc(vcpu, 3);
> - return 0;
> - }
> + /* Bailout forbidden function codes */
> + if (fc > 3 && fc != 15)
> + goto out_no_data;
> +
> + /* fc 15 is provided with PTF/CPU topology support */
> + if (fc == 15 && !test_kvm_facility(vcpu->kvm, 11))
> + goto out_no_data;
>
> if (vcpu->run->s.regs.gprs[0] & 0x0fffff00
> || vcpu->run->s.regs.gprs[1] & 0xffff0000)
> @@ -910,6 +913,10 @@ 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,
> diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c
> index dada78b92691..4f4fee697550 100644
> --- a/arch/s390/kvm/vsie.c
> +++ b/arch/s390/kvm/vsie.c
> @@ -503,6 +503,9 @@ static int shadow_scb(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
> /* Host-protection-interruption introduced with ESOP */
> if (test_kvm_cpu_feat(vcpu->kvm, KVM_S390_VM_CPU_FEAT_ESOP))
> scb_s->ecb |= scb_o->ecb & ECB_HOSTPROTINT;
> + /* CPU Topology */

Maybe also add:
This facility only uses the utility field of the SCA and none of the cpu
entries that are problematic with the other interpretation facilities so
we can pass it through.

> + if (test_kvm_facility(vcpu->kvm, 11))
> + scb_s->ecb |= scb_o->ecb & ECB_PTF;
> /* transactional execution */
> if (test_kvm_facility(vcpu->kvm, 73) && wants_tx) {
> /* remap the prefix is tx is toggled on */

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