Re: [PATCH v10 2/3] KVM: s390: guest support for topology function

From: Janosch Frank
Date: Fri Jun 24 2022 - 02:22:46 EST

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@xxxxxxxxxxxxx>
---
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 */