linux-kernel - [PATCH v4 0/5] KVM: x86: Partially allow KVM_SET_CPUID{,2} after KVM

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Date:   Fri, 21 Jan 2022 14:28:47 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Igor Mammedov <imammedo@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v4 0/5] KVM: x86: Partially allow KVM_SET_CPUID{,2} after KVM_RUN for CPU hotplug

Changes since v3:
- Use memcmp() [Sean].
- Update the comment in kvm_set_cpuid() making (hopefully) it more clear
 that the introduced check does not cover all potentially problemmatic
 scenarios [Sean].
- Add "KVM: x86: Move CPUID.(EAX=0x12,ECX=1) mangling to
 __kvm_update_cpuid_runtime()" patch.

Original description:

Recently, KVM made it illegal to change CPUID after KVM_RUN but
unfortunately this change is not fully compatible with existing VMMs.
In particular, QEMU reuses vCPU fds for CPU hotplug after unplug and it
calls KVM_SET_CPUID2. Relax the requirement by implementing an allowing
KVM_SET_CPUID{,2} with the exact same data.

Vitaly Kuznetsov (5):
  KVM: x86: Do runtime CPUID update before updating
    vcpu->arch.cpuid_entries
  KVM: x86: Move CPUID.(EAX=0x12,ECX=1) mangling to
    __kvm_update_cpuid_runtime()
  KVM: x86: Partially allow KVM_SET_CPUID{,2} after KVM_RUN
  KVM: selftests: Rename 'get_cpuid_test' to 'cpuid_test'
  KVM: selftests: Test KVM_SET_CPUID2 after KVM_RUN

 arch/x86/kvm/cpuid.c                          | 119 +++++++++++++-----
 arch/x86/kvm/x86.c                            |  19 ---
 tools/testing/selftests/kvm/.gitignore        |   2 +-
 tools/testing/selftests/kvm/Makefile          |   4 +-
 .../selftests/kvm/include/x86_64/processor.h  |   7 ++
 .../selftests/kvm/lib/x86_64/processor.c      |  33 ++++-
 .../x86_64/{get_cpuid_test.c => cpuid_test.c} |  30 +++++
 7 files changed, 157 insertions(+), 57 deletions(-)
 rename tools/testing/selftests/kvm/x86_64/{get_cpuid_test.c => cpuid_test.c} (83%)

-- 
2.34.1