Re: [Xen-devel] [PATCH 2/3] VMX: don't blindly enable descriptor table exiting control

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 13/04/17 15:53, Jan Beulich wrote:
> @@ -223,9 +223,15 @@ int arch_monitor_domctl_event(struct dom
>          ad->monitor.descriptor_access_enabled = requested_status;
>  
>          for_each_vcpu ( d, v )
> -            hvm_funcs.set_descriptor_access_exiting(v, requested_status);
> +        {
> +            ok = hvm_funcs.set_descriptor_access_exiting(v, 
> requested_status);
> +            if ( !ok )
> +                break;
> +        }
>  
>          domain_unpause(d);
> +        if ( !ok )
> +            return -EOPNOTSUPP;

While the overall purpose of the patch is clearly a good thing, this
implementation isn't ideal.

In principle, this structure could hit a failure mid way through the
vcpus, leaving them in an inconsistent state.

Instead, why not clobber the set_descriptor_access_exiting() function
pointer if support isn't available, and use that (before the
domain_pause()) to fail with EOPNOTSUPP?

~Andrew

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