Re: [PATCH v3 2/6] KVM: nVMX: Keep KVM updates to PERF_GLOBAL_CTRL ctrl bits across MSR write

[Oliver Upton <oupton@google.com>]

On Fri, Feb 25, 2022 at 08:08:19PM +0000, Oliver Upton wrote:
> 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.
> 
> Uphold the old ABI by reapplying KVM's tweaks to the BNDCFGS bits after
> an MSR write from userspace.
>

typo: s/BNDCFGS/"load IA32_PERF_GLOBAL_CTRL"/

I'll adopt this if I need to send another spin of the series. Otherwise,
do you mind fixing the typo when applying Paolo?

--
Oliver