KVM: x86: Partially allow KVM_SET_CPUID{,2} after KVM_RUN

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Commit feb627e8d6 ("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: Igor Mammedov <imammedo@redhat.com>
Fixes: feb627e8d6 ("KVM: x86: Forbid KVM_SET_CPUID{,2} after KVM_RUN")
Signed-off-by: Vitaly 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: Paolo Bonzini <pbonzini@redhat.com>

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Vitaly Kuznetsov 2022-01-17 16:05:40 +01:00 • committed by Paolo Bonzini

parent ee3a5f9e3d

commit c6617c61e8

2 changed files with 36 additions and 19 deletions

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36

arch/x86/kvm/cpuid.c

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19

arch/x86/kvm/x86.c

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