Commit feb627e8 ("KVM: x86: Forbid KVM_SET_CPUID{,2} after KVM_RUN")
forbade changing CPUID altogether but unfortunately this is not fully
compatible with existing VMMs. In particular, QEMU reuses vCPU fds for
CPU hotplug after unplug and it calls KVM_SET_CPUID2. Instead of full ban,
check whether the supplied CPUID data is equal to what was previously set.
Reported-by: NIgor Mammedov <imammedo@redhat.com>
Fixes: feb627e8 ("KVM: x86: Forbid KVM_SET_CPUID{,2} after KVM_RUN")
Signed-off-by: NVitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20220117150542.2176196-3-vkuznets@redhat.com>
Cc: stable@vger.kernel.org
[Do not call kvm_find_cpuid_entry repeatedly. - Paolo]
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>