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KVM: X86: Reset vcpu->arch.cpuid_nent to 0 if SET_CPUID* fails 

Current implementation keeps userspace input of CPUID configuration and
cpuid->nent even if kvm_update_cpuid() fails. Reset vcpu->arch.cpuid_nent
to 0 for the case of failure as a simple fix.

Besides, update the doc to explicitly state that if IOCTL SET_CPUID*
fail KVM gives no gurantee that previous valid CPUID configuration is
kept.

Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
Message-Id: <20200708065054.19713-2-xiaoyao.li@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Xiaoyao Li 2020-07-08 14:50:47 +08:00 committed by Paolo Bonzini
parent 2e8cd7a3b8
commit 1896409282
2 changed files with 8 additions and 0 deletions
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4
Documentation/virt/kvm/api.rst
View File

@ -669,6 +669,10 @@ MSRs that have been set successfully.
Defines the vcpu responses to the cpuid instruction. Applications
should use the KVM_SET_CPUID2 ioctl if available.
Note, when this IOCTL fails, KVM gives no guarantees that previous valid CPUID
configuration (if there is) is not corrupted. Userspace can get a copy of the
resulting CPUID configuration through KVM_GET_CPUID2 in case.
::
struct kvm_cpuid_entry {

4
arch/x86/kvm/cpuid.c
View File

@ -209,6 +209,8 @@ int kvm_vcpu_ioctl_set_cpuid(struct kvm_vcpu *vcpu,
kvm_apic_set_version(vcpu);
kvm_x86_ops.cpuid_update(vcpu);
r = kvm_update_cpuid(vcpu);
if (r)
vcpu->arch.cpuid_nent = 0;
kvfree(cpuid_entries);
out:
@ -232,6 +234,8 @@ int kvm_vcpu_ioctl_set_cpuid2(struct kvm_vcpu *vcpu,
kvm_apic_set_version(vcpu);
kvm_x86_ops.cpuid_update(vcpu);
r = kvm_update_cpuid(vcpu);
if (r)
vcpu->arch.cpuid_nent = 0;
out:
return r;
}