Re: [PATCH v5 2/2] x86/xen: Allow per-domain usage of hardware virtualized APIC

[Jane Malalane <Jane.Malalane@citrix.com>]

On 08/03/2022 12:33, Roger Pau Monné wrote:
> On Tue, Mar 08, 2022 at 01:24:23PM +0100, Jan Beulich wrote:
>> On 08.03.2022 12:38, Roger Pau Monné wrote:
>>> On Mon, Mar 07, 2022 at 03:06:09PM +0000, Jane Malalane wrote:
>>>> @@ -685,13 +687,31 @@ int arch_sanitise_domain_config(struct xen_domctl_createdomain *config)
>>>>           }
>>>>       }
>>>>   
>>>> -    if ( config->arch.misc_flags & ~XEN_X86_MSR_RELAXED )
>>>> +    if ( config->arch.misc_flags & ~(XEN_X86_MSR_RELAXED |
>>>> +                                     XEN_X86_ASSISTED_XAPIC |
>>>> +                                     XEN_X86_ASSISTED_X2APIC) )
>>>>       {
>>>>           dprintk(XENLOG_INFO, "Invalid arch misc flags %#x\n",
>>>>                   config->arch.misc_flags);
>>>>           return -EINVAL;
>>>>       }
>>>>   
>>>> +    if ( (assisted_xapic || assisted_x2apic) && !hvm )
>>>> +    {
>>>> +        dprintk(XENLOG_INFO,
>>>> +                "Interrupt Controller Virtualization not supported for PV\n");
>>>> +        return -EINVAL;
>>>> +    }
>>>> +
>>>> +    if ( (assisted_xapic && !assisted_xapic_available) ||
>>>> +         (assisted_x2apic && !assisted_x2apic_available) )
>>>> +    {
>>>> +        dprintk(XENLOG_INFO,
>>>> +                "Hardware assisted x%sAPIC requested but not available\n",
>>>> +                assisted_xapic && !assisted_xapic_available ? "" : "2");
>>>> +        return -EINVAL;
>>>
>>> I think for those two you could return -ENODEV if others agree.
>>
>> If by "two" you mean the xAPIC and x2APIC aspects here (and not e.g. this
>> and the earlier if()), then I agree. I'm always in favor of using distinct
>> error codes when possible and at least halfway sensible.
> 
> I would be fine by using it for the !hvm if also. IMO it makes sense
> as PV doesn't have an APIC 'device' at all, so ENODEV would seem
> fitting. EINVAL is also fine as the caller shouldn't even attempt that
> in the first place.
> 
> So let's use it for the last if only.
Wouldn't it make more sense to use -ENODEV particularly for the first? I 
agree that -ENODEV should be reported in the first case because it 
doesn't make sense to request acceleration of something that doesn't 
exist and I should have put that. But having a look at the hap code 
(since it resembles the second case), it returns -EINVAL when it is not 
available, unless you deem this to be different or, in retrospective, 
that the hap code should too have been coded to return -ENODEV.

if ( hap && !hvm_hap_supported() )
     {
         dprintk(XENLOG_INFO, "HAP requested but not available\n");
         return -EINVAL;
     }

I agree with all the other comments and have made the approp changes for 
v6. Thanks a lot.

Jane.