[PATCH v2 2/7] KVM: nVMX: Keep KVM updates to PERF_GLOBAL_CTRL ctrl bits across MSR write

Oliver Upton
2022-02-04T20:47:14Z

Since commit 03a8871add95 ("KVM: nVMX: Expose load IA32_PERF_GLOBAL_CTRL
VM-{Entry,Exit} control"), KVM has taken ownership of the "load
IA32_PERF_GLOBAL_CTRL" VMX entry/exit control bits. The ABI is that
these bits will be set in the IA32_VMX_TRUE_{ENTRY,EXIT}_CTLS MSRs if
the guest's CPUID exposes a vPMU that supports the IA32_PERF_GLOBAL_CTRL
MSR (CPUID.0AH:EAX[7:0] > 1), and clear otherwise.

However, KVM will only do so if userspace sets the CPUID before writing
to the corresponding MSRs. Of course, there are no ordering requirements
between these ioctls. Uphold the ABI regardless of ordering by
reapplying KVMs tweaks to the VMX control MSRs after userspace has
written to them.

Note that older kernels without commit c44d9b34701d ("KVM: x86: Invoke
vendor's vcpu_after_set_cpuid() after all common updates") still require
that the entry/exit controls be updated from kvm_pmu_refresh(). Leave
the benign call in place to allow for cleaner backporting and punt the
cleanup to a later change.

Fixes: 03a8871add95 ("KVM: nVMX: Expose load IA32_PERF_GLOBAL_CTRL VM-{Entry,Exit} control")
Reported-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Oliver Upton <oupton@google.com>
---
arch/x86/kvm/vmx/vmx.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index d63d6dfbadbf..54ac382a0b73 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7242,6 +7242,8 @@ void nested_vmx_entry_exit_ctls_update(struct kvm_vcpu *vcpu)
vmx->nested.msrs.exit_ctls_high &= ~VM_EXIT_CLEAR_BNDCFGS;
}
}
+
+ nested_vmx_pmu_entry_exit_ctls_update(vcpu);
}

static void update_intel_pt_cfg(struct kvm_vcpu *vcpu)
--
2.35.0.263.gb82422642f-goog