Commit 59461b8c authored by Zeng Guang's avatar Zeng Guang Committed by Jason Zeng
Browse files

KVM: x86: Allow userspace to set maximum VCPU id for VM 

mainline inclusion
from mainline-v6.0-rc1
commit 35875316
category: feature
feature: IPI Virtualization
bugzilla: https://gitee.com/openeuler/intel-kernel/issues/I5ODSC
CVE: N/A
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=35875316384b71d23dc2a45a969732fc8cab16af



Intel-SIG: commit 35875316 ("KVM: x86: Allow userspace to set maximum VCPU id for VM")

-------------------------------------

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_ID.

Suggested-by: default avatarSean Christopherson <seanjc@google.com>
Reviewed-by: default avatarMaxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: default avatarZeng Guang <guang.zeng@intel.com>
Message-Id: <20220419154444.11888-1-guang.zeng@intel.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: default avatarJason Zeng <jason.zeng@intel.com>

Signed-off-by: default avatarJason Zeng <jason.zeng@intel.com>
parent c8477db6

Documentation/virt/kvm/api.rst

+21 −0
Original line number Diff line number Diff line
@@ -6220,6 +6220,27 @@ default. 


See Documentation/x86/sgx.rst for more details.



7.23 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_ID

          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.

======================

arch/x86/include/asm/kvm_host.h

+6 −0
Original line number Diff line number Diff line
@@ -1020,6 +1020,12 @@ struct kvm_arch { 
	struct list_head tdp_mmu_roots;

	/* List of struct tdp_mmu_pages not being used as roots */

	struct list_head tdp_mmu_pages;

	/*

	 * VM-scope maximum vCPU ID. Used to determine the size of structures

	 * that increase along with the maximum vCPU ID, in which case, using

	 * the global KVM_MAX_VCPU_ID may lead to significant memory waste.

	 */

	u32 max_vcpu_ids;

};



struct kvm_vm_stat {

arch/x86/kvm/x86.c

+20 −0
Original line number Diff line number Diff line
@@ -5432,6 +5432,20 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm, 
		break;

	}

#endif

	case KVM_CAP_MAX_VCPU_ID:

		r = -EINVAL;

		if (cap->args[0] > KVM_MAX_VCPU_ID)

			break;



		mutex_lock(&kvm->lock);

		if (kvm->arch.max_vcpu_ids == cap->args[0]) {

			r = 0;

		} else if (!kvm->arch.max_vcpu_ids) {

			kvm->arch.max_vcpu_ids = cap->args[0];

			r = 0;

		}

		mutex_unlock(&kvm->lock);

		break;

	default:

		r = -EINVAL;

		break;
@@ -10106,6 +10120,12 @@ int kvm_arch_vcpu_precreate(struct kvm *kvm, unsigned int id) 
		pr_warn_once("kvm: SMP vm created on host with unstable TSC; "

			     "guest TSC will not be reliable\n");



	if (!kvm->arch.max_vcpu_ids)

		kvm->arch.max_vcpu_ids = KVM_MAX_VCPU_ID;



	if (id >= kvm->arch.max_vcpu_ids)

		return -EINVAL;



	return 0;

}