Re: [Xen-devel] [PATCH] x86/altp2m: add altp2m_vcpu_disable_notify

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 14.12.18 at 18:17, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
> Allow altp2m users to disable #VE/VMFUNC alone. Currently it is
> only possible to disable this functionality when we disable altp2m
> completely; #VE/VMFUNC can only be enabled once per altp2m session.
> 
> In addition to making things complete, disabling #VE is also a
> workaround for CFW116 ("When Virtualization Exceptions are Enabled,
> EPT Violations May Generate Erroneous Virtualization Exceptions")
> on Xeon CPUs.

"Xeon CPUs" is overly generic. Yes, the CFW erratum prefix allows
to identify which one you mean, but only (afaik) by going through
the spec updates until you've found the right one. Can you please
be more specific here?

> @@ -4602,6 +4603,36 @@ static int do_altp2m_op(
>          break;
>      }
>  
> +    case HVMOP_altp2m_vcpu_disable_notify:
> +    {
> +        struct vcpu *v;
> +
> +        if ( a.u.disable_notify.pad ||
> +             a.u.disable_notify.vcpu_id >= d->max_vcpus )
> +        {
> +            rc = -EINVAL;
> +            break;
> +        }
> +
> +        if ( !cpu_has_vmx_virt_exceptions )
> +        {
> +            rc = -EOPNOTSUPP;
> +            break;
> +        }
> +
> +        v = d->vcpu[a.u.enable_notify.vcpu_id];
> +
> +        if ( gfn_eq(vcpu_altp2m(v).veinfo_gfn, INVALID_GFN) )
> +        {
> +            rc = -EINVAL;
> +            break;
> +        }

Why? Disabling what is already disabled is not wrong, and hence
could easily be treated as a no-op.

> --- a/xen/include/public/hvm/hvm_op.h
> +++ b/xen/include/public/hvm/hvm_op.h
> @@ -232,6 +232,13 @@ struct xen_hvm_altp2m_vcpu_enable_notify {
>  typedef struct xen_hvm_altp2m_vcpu_enable_notify 
> xen_hvm_altp2m_vcpu_enable_notify_t;
>  DEFINE_XEN_GUEST_HANDLE(xen_hvm_altp2m_vcpu_enable_notify_t);
>  
> +struct xen_hvm_altp2m_vcpu_disable_notify {
> +    uint32_t vcpu_id;
> +    uint32_t pad;

Why the pad field? There's no hole left.

Jan



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