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| author | Sean Christopherson <seanjc@google.com> | 2024-08-02 11:55:05 -0700 |
|---|---|---|
| committer | Sean Christopherson <seanjc@google.com> | 2024-11-01 09:22:31 -0700 |
| commit | dcb988cdac85bad177de86fbf409524eda4f9467 (patch) | |
| tree | 568a19ac2ef88c59979327c44f8e0d5390313bd4 /Documentation/virt | |
| parent | bc2ca3680b30869ee9a764ab72c143070f1afec8 (diff) | |
| download | ath-dcb988cdac85bad177de86fbf409524eda4f9467.tar.gz | |
KVM: x86: Quirk initialization of feature MSRs to KVM's max configuration
Add a quirk to control KVM's misguided initialization of select feature
MSRs to KVM's max configuration, as enabling features by default violates
KVM's approach of letting userspace own the vCPU model, and is actively
problematic for MSRs that are conditionally supported, as the vCPU will
end up with an MSR value that userspace can't restore. E.g. if the vCPU
is configured with PDCM=0, userspace will save and attempt to restore a
non-zero PERF_CAPABILITIES, thanks to KVM's meddling.
Link: https://lore.kernel.org/r/20240802185511.305849-4-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Diffstat (limited to 'Documentation/virt')
| -rw-r--r-- | Documentation/virt/kvm/api.rst | 22 |
1 files changed, 22 insertions, 0 deletions
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index edc070c6e19b2..061ec93d9ecb7 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -8107,6 +8107,28 @@ KVM_X86_QUIRK_SLOT_ZAP_ALL By default, for KVM_X86_DEFAULT_VM VMs, KVM or moved memslot isn't reachable, i.e KVM _may_ invalidate only SPTEs related to the memslot. + +KVM_X86_QUIRK_STUFF_FEATURE_MSRS By default, at vCPU creation, KVM sets the + vCPU's MSR_IA32_PERF_CAPABILITIES (0x345), + MSR_IA32_ARCH_CAPABILITIES (0x10a), + MSR_PLATFORM_INFO (0xce), and all VMX MSRs + (0x480..0x492) to the maximal capabilities + supported by KVM. KVM also sets + MSR_IA32_UCODE_REV (0x8b) to an arbitrary + value (which is different for Intel vs. + AMD). Lastly, when guest CPUID is set (by + userspace), KVM modifies select VMX MSR + fields to force consistency between guest + CPUID and L2's effective ISA. When this + quirk is disabled, KVM zeroes the vCPU's MSR + values (with two exceptions, see below), + i.e. treats the feature MSRs like CPUID + leaves and gives userspace full control of + the vCPU model definition. This quirk does + not affect VMX MSRs CR0/CR4_FIXED1 (0x487 + and 0x489), as KVM does now allow them to + be set by userspace (KVM sets them based on + guest CPUID, for safety purposes). =================================== ============================================ 7.32 KVM_CAP_MAX_VCPU_ID |