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KVM: s390: Do not report unusabled IDs via KVM_CAP_MAX_VCPU_ID

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commit a86cb413f4bf273a9d341a3ab2c2ca44e12eb317 upstream.

KVM_CAP_MAX_VCPU_ID is currently always reporting KVM_MAX_VCPU_ID on all
architectures. However, on s390x, the amount of usable CPUs is determined
during runtime - it is depending on the features of the machine the code
is running on. Since we are using the vcpu_id as an index into the SCA
structures that are defined by the hardware (see e.g. the sca_add_vcpu()
function), it is not only the amount of CPUs that is limited by the hard-
ware, but also the range of IDs that we can use.
Thus KVM_CAP_MAX_VCPU_ID must be determined during runtime on s390x, too.
So the handling of KVM_CAP_MAX_VCPU_ID has to be moved from the common
code into the architecture specific code, and on s390x we have to return
the same value here as for KVM_CAP_MAX_VCPUS.
This problem has been discovered with the kvm_create_max_vcpus selftest.
With this change applied, the selftest now passes on s390x, too.

Reviewed-by: Andrew Jones <drjones@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20190523164309.13345-9-thuth@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Thomas Huth 2019-05-23 18:43:08 +02:00 • committed by Greg Kroah-Hartman
commit 6a2fbec707
2 changed files with 13 additions and 2 deletions
Download patch file Download diff file Expand all files Collapse all files

3
virt/kvm/arm/arm.c
View file

@ -223,6 +223,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
case KVM_CAP_MAX_VCPUS:
r = KVM_MAX_VCPUS;
break;
case KVM_CAP_MAX_VCPU_ID:
r = KVM_MAX_VCPU_ID;
break;
case KVM_CAP_NR_MEMSLOTS:
r = KVM_USER_MEM_SLOTS;
break;

2
virt/kvm/kvm_main.c
View file

@ -2965,8 +2965,6 @@ static long kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg)
case KVM_CAP_MULTI_ADDRESS_SPACE:
return KVM_ADDRESS_SPACE_NUM;
#endif
case KVM_CAP_MAX_VCPU_ID:
return KVM_MAX_VCPU_ID;
default:
break;
}