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authorZeng Guang <guang.zeng@intel.com>2022-04-19 23:44:44 +0800
committerPaolo Bonzini <pbonzini@redhat.com>2022-06-08 04:47:31 -0400
commit35875316384b71d23dc2a45a969732fc8cab16af (patch)
tree68c6884064bf6e7827c802d9b72aff9b966df290 /Documentation/virt
parent1d5e740d518e02cea46325b3d37135bf9c08982a (diff)
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')
-rw-r--r--Documentation/virt/kvm/api.rst21
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.
======================