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| author | Zeng Guang <guang.zeng@intel.com> | 2022-04-19 18:44:44 +0300 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2022-06-08 11:47:31 +0300 |
| commit | 35875316384b71d23dc2a45a969732fc8cab16af (patch) | |
| tree | 68c6884064bf6e7827c802d9b72aff9b966df290 /Documentation/virt/kvm/api.rst | |
| parent | 1d5e740d518e02cea46325b3d37135bf9c08982a (diff) | |
| download | linux-35875316384b71d23dc2a45a969732fc8cab16af.tar.xz | |
KVM: x86: Allow userspace to set maximum VCPU id for VM
Introduce new max_vcpu_ids in KVM for x86 architecture. Userspace
can assign maximum possible vcpu id for current VM session using
KVM_CAP_MAX_VCPU_ID of KVM_ENABLE_CAP ioctl().
This is done for x86 only because the sole use case is to guide
memory allocation for PID-pointer table, a structure needed to
enable VMX IPI.
By default, max_vcpu_ids set as KVM_MAX_VCPU_IDS.
Suggested-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: Zeng Guang <guang.zeng@intel.com>
Message-Id: <20220419154444.11888-1-guang.zeng@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'Documentation/virt/kvm/api.rst')
| -rw-r--r-- | Documentation/virt/kvm/api.rst | 21 |
1 files changed, 21 insertions, 0 deletions
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index 94d73ec52aba..421479a67da5 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -7494,6 +7494,27 @@ The valid bits in cap.args[0] are: generate a #UD within the guest. =================================== ============================================ +7.32 KVM_CAP_MAX_VCPU_ID +------------------------ + +:Architectures: x86 +:Target: VM +:Parameters: args[0] - maximum APIC ID value set for current VM +:Returns: 0 on success, -EINVAL if args[0] is beyond KVM_MAX_VCPU_IDS + supported in KVM or if it has been set. + +This capability allows userspace to specify maximum possible APIC ID +assigned for current VM session prior to the creation of vCPUs, saving +memory for data structures indexed by the APIC ID. Userspace is able +to calculate the limit to APIC ID values from designated +CPU topology. + +The value can be changed only until KVM_ENABLE_CAP is set to a nonzero +value or until a vCPU is created. Upon creation of the first vCPU, +if the value was set to zero or KVM_ENABLE_CAP was not invoked, KVM +uses the return value of KVM_CHECK_EXTENSION(KVM_CAP_MAX_VCPU_ID) as +the maximum APIC ID. + 8. Other capabilities. ====================== |