Re: [PATCH v3 3/4] kvm: vmx: Add last_cpu to struct vcpu_vmx

[Sean Christopherson <sean.j.christopherson@intel.com>]

On Mon, Jun 01, 2020 at 03:24:15PM -0700, Jim Mattson wrote:
> As we already do in svm, record the last logical processor on which a
> vCPU has run, so that it can be communicated to userspace for
> potential hardware errors.
> 
> Signed-off-by: Jim Mattson <jmattson@google.com>
> Reviewed-by: Oliver Upton <oupton@google.com>
> Reviewed-by: Peter Shier <pshier@google.com>
> ---
>  arch/x86/kvm/vmx/vmx.c | 1 +
>  arch/x86/kvm/vmx/vmx.h | 3 +++
>  2 files changed, 4 insertions(+)
> 
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 170cc76a581f..42856970d3b8 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -6730,6 +6730,7 @@ static fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu)
>  	if (vcpu->arch.cr2 != read_cr2())
>  		write_cr2(vcpu->arch.cr2);
>  
> +	vmx->last_cpu = vcpu->cpu;

This is redundant in the EXIT_FASTPATH_REENTER_GUEST case.  Setting it
before reenter_guest is technically wrong if emulation_required is true, but
that doesn't seem like it'd be an issue in practice.

>  	vmx->fail = __vmx_vcpu_run(vmx, (unsigned long *)&vcpu->arch.regs,
>  				   vmx->loaded_vmcs->launched);
>  
> diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
> index 672c28f17e49..8a1e833cf4fb 100644
> --- a/arch/x86/kvm/vmx/vmx.h
> +++ b/arch/x86/kvm/vmx/vmx.h
> @@ -302,6 +302,9 @@ struct vcpu_vmx {
>  	u64 ept_pointer;
>  
>  	struct pt_desc pt_desc;
> +
> +	/* which host CPU was used for running this vcpu */
> +	unsigned int last_cpu;

Why not put this in struct kvm_vcpu_arch?  I'd also vote to name it
last_run_cpu, as last_cpu is super misleading.

And if it's in arch, what about setting it vcpu_enter_guest?

>  };
>  
>  enum ept_pointers_status {
> -- 
> 2.27.0.rc2.251.g90737beb825-goog
>