Re: [PATCH v10 3/3] KVM: s390: resetting the Topology-Change-Report
From: Janosch Frank
Date: Fri Jun 24 2022 - 02:51:00 EST
On 6/20/22 14:54, Pierre Morel wrote:
During a subsystem reset the Topology-Change-Report is cleared.
Let's give userland the possibility to clear the MTCR in the case
of a subsystem reset.
To migrate the MTCR, we give userland the possibility to
query the MTCR state.
We indicate KVM support for the CPU topology facility with a new
KVM capability: KVM_CAP_S390_CPU_TOPOLOGY.
Signed-off-by: Pierre Morel <pmorel@xxxxxxxxxxxxx>
---
Documentation/virt/kvm/api.rst | 31 +++++++++++
arch/s390/include/uapi/asm/kvm.h | 10 ++++
arch/s390/kvm/kvm-s390.c | 96 ++++++++++++++++++++++++++++++++
include/uapi/linux/kvm.h | 1 +
4 files changed, 138 insertions(+)
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 11e00a46c610..326f8b7e7671 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -7956,6 +7956,37 @@ should adjust CPUID leaf 0xA to reflect that the PMU is disabled.
When enabled, KVM will exit to userspace with KVM_EXIT_SYSTEM_EVENT of
type KVM_SYSTEM_EVENT_SUSPEND to process the guest suspend request.
+8.37 KVM_CAP_S390_CPU_TOPOLOGY
+------------------------------
+
+:Capability: KVM_CAP_S390_CPU_TOPOLOGY
+:Architectures: s390
+:Type: vm
+
+This capability indicates that KVM will provide the S390 CPU Topology
+facility which consist of the interpretation of the PTF instruction for
+the Function Code 2 along with interception and forwarding of both the
Making function code capital surprises me when reading.
+PTF instruction with Function Codes 0 or 1 and the STSI(15,1,x)
+instruction to the userland hypervisor.
+
+The stfle facility 11, CPU Topology facility, should not be provided
s/provided/indicated
+to the guest without this capability.
+
+When this capability is present, KVM provides a new attribute group
+on vm fd, KVM_S390_VM_CPU_TOPOLOGY.
+This new attribute allows to get, set or clear the Modified Change
+Topology Report (MTCR) bit of the SCA through the kvm_device_attr
+structure.
+
+Getting the MTCR bit is realized by using a kvm_device_attr attr
+entry value of KVM_GET_DEVICE_ATTR and with kvm_device_attr addr
+entry pointing to the address of a struct kvm_cpu_topology.
+The value of the MTCR is return by the bit mtcr of the structure. > +
+When using KVM_SET_DEVICE_ATTR the MTCR is set by using the
+attr->attr value KVM_S390_VM_CPU_TOPO_MTCR_SET and cleared by
+using KVM_S390_VM_CPU_TOPO_MTCR_CLEAR.
I have the feeling that we can drop the two blocks above and we won't
loose information.
+/**
+ * kvm_s390_sca_clear_mtcr
+ * @kvm: guest KVM description
+ *
+ * Is only relevant if the topology facility is present,
+ * the caller should check KVM facility 11
+ *
+ * Updates the Multiprocessor Topology-Change-Report to signal
+ * the guest with a topology change.
+ */
+static void kvm_s390_sca_clear_mtcr(struct kvm *kvm)
This is a set operation with the value 0 and that's clearly visible by
the copied code. If you make the utility entry a bitfield you can easily
set 0/1 via one function without doing the bit manipulation by hand.
I.e. please only use one set function.
+{
+ struct bsca_block *sca = kvm->arch.sca; /* SCA version doesn't matter */
+
+ ipte_lock(kvm);
+ sca->utility &= ~SCA_UTILITY_MTCR;
+ ipte_unlock(kvm);
+}
+
+static int kvm_s390_set_topology(struct kvm *kvm, struct kvm_device_attr *attr)
+{
+ if (!test_kvm_facility(kvm, 11))
+ return -ENXIO;
+
+ switch (attr->attr) {
+ case KVM_S390_VM_CPU_TOPO_MTCR_SET:
+ kvm_s390_sca_set_mtcr(kvm);
+ break;
+ case KVM_S390_VM_CPU_TOPO_MTCR_CLEAR:
+ kvm_s390_sca_clear_mtcr(kvm);
+ break;
+ }
By having two endpoints here we trade an easy check with having to
access process memory to grab the value we want to set.
I'm still torn about this.
+ return 0;
+}
+
+/**
+ * kvm_s390_sca_get_mtcr
+ * @kvm: guest KVM description
+ *
+ * Is only relevant if the topology facility is present,
+ * the caller should check KVM facility 11
+ *
+ * reports to QEMU the Multiprocessor Topology-Change-Report.
+ */
+static int kvm_s390_sca_get_mtcr(struct kvm *kvm)
+{
+ struct bsca_block *sca = kvm->arch.sca; /* SCA version doesn't matter */
Same comments as with the set_mtcr()
+ int val;
+
+ ipte_lock(kvm);
+ val = sca->utility & SCA_UTILITY_MTCR;
+ ipte_unlock(kvm);
+
+ return val;
+}
+
+static int kvm_s390_get_topology(struct kvm *kvm, struct kvm_device_attr *attr)
+{
+ struct kvm_cpu_topology topo = {};
+
+ if (!test_kvm_facility(kvm, 11))
+ return -ENXIO;
+
+ topo.mtcr = kvm_s390_sca_get_mtcr(kvm) ? 1 : 0;
+ if (copy_to_user((void __user *)attr->addr, &topo, sizeof(topo)))
+ return -EFAULT;
+
+ return 0;
+}
+
static int kvm_s390_vm_set_attr(struct kvm *kvm, struct kvm_device_attr *attr)
{
int ret;
@@ -1730,6 +1817,9 @@ static int kvm_s390_vm_set_attr(struct kvm *kvm, struct kvm_device_attr *attr)
case KVM_S390_VM_MIGRATION:
ret = kvm_s390_vm_set_migration(kvm, attr);
break;
+ case KVM_S390_VM_CPU_TOPOLOGY:
+ ret = kvm_s390_set_topology(kvm, attr);
+ break;
default:
ret = -ENXIO;
break;
@@ -1755,6 +1845,9 @@ static int kvm_s390_vm_get_attr(struct kvm *kvm, struct kvm_device_attr *attr)
case KVM_S390_VM_MIGRATION:
ret = kvm_s390_vm_get_migration(kvm, attr);
break;
+ case KVM_S390_VM_CPU_TOPOLOGY:
+ ret = kvm_s390_get_topology(kvm, attr);
+ break;
default:
ret = -ENXIO;
break;
@@ -1828,6 +1921,9 @@ static int kvm_s390_vm_has_attr(struct kvm *kvm, struct kvm_device_attr *attr)
case KVM_S390_VM_MIGRATION:
ret = 0;
break;
+ case KVM_S390_VM_CPU_TOPOLOGY:
+ ret = test_kvm_facility(kvm, 11) ? 0 : -ENXIO;
+ break;
default:
ret = -ENXIO;
break;
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 5088bd9f1922..33317d820032 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1157,6 +1157,7 @@ struct kvm_ppc_resize_hpt {
#define KVM_CAP_VM_TSC_CONTROL 214
#define KVM_CAP_SYSTEM_EVENT_DATA 215
#define KVM_CAP_ARM_SYSTEM_SUSPEND 216
+#define KVM_CAP_S390_CPU_TOPOLOGY 217
#ifdef KVM_CAP_IRQ_ROUTING