Re: [PATCH for-4.19 v3 2/3] xen: enable altp2m at create domain domctl

[Jan Beulich <jbeulich@xxxxxxxx>]

On 22.05.2024 15:16, Roger Pau Monné wrote:
> On Tue, May 21, 2024 at 12:30:32PM +0200, Jan Beulich wrote:
>> On 17.05.2024 15:33, Roger Pau Monne wrote:
>>> Enabling it using an HVM param is fragile, and complicates the logic when
>>> deciding whether options that interact with altp2m can also be enabled.
>>>
>>> Leave the HVM param value for consumption by the guest, but prevent it from
>>> being set.  Enabling is now done using and additional altp2m specific field 
>>> in
>>> xen_domctl_createdomain.
>>>
>>> Note that albeit only currently implemented in x86, altp2m could be 
>>> implemented
>>> in other architectures, hence why the field is added to 
>>> xen_domctl_createdomain
>>> instead of xen_arch_domainconfig.
>>>
>>> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
>>
>> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx> # hypervisor
>> albeit with one question:
>>
>>> --- a/xen/arch/x86/domain.c
>>> +++ b/xen/arch/x86/domain.c
>>> @@ -637,6 +637,8 @@ int arch_sanitise_domain_config(struct 
>>> xen_domctl_createdomain *config)
>>>      bool hap = config->flags & XEN_DOMCTL_CDF_hap;
>>>      bool nested_virt = config->flags & XEN_DOMCTL_CDF_nested_virt;
>>>      unsigned int max_vcpus;
>>> +    unsigned int altp2m_mode = MASK_EXTR(config->altp2m_opts,
>>> +                                         XEN_DOMCTL_ALTP2M_mode_mask);
>>>  
>>>      if ( hvm ? !hvm_enabled : !IS_ENABLED(CONFIG_PV) )
>>>      {
>>> @@ -715,6 +717,26 @@ int arch_sanitise_domain_config(struct 
>>> xen_domctl_createdomain *config)
>>>          return -EINVAL;
>>>      }
>>>  
>>> +    if ( config->altp2m_opts & ~XEN_DOMCTL_ALTP2M_mode_mask )
>>> +    {
>>> +        dprintk(XENLOG_INFO, "Invalid altp2m options selected: %#x\n",
>>> +                config->flags);
>>> +        return -EINVAL;
>>> +    }
>>> +
>>> +    if ( altp2m_mode && nested_virt )
>>> +    {
>>> +        dprintk(XENLOG_INFO,
>>> +                "Nested virt and altp2m are not supported together\n");
>>> +        return -EINVAL;
>>> +    }
>>> +
>>> +    if ( altp2m_mode && !hap )
>>> +    {
>>> +        dprintk(XENLOG_INFO, "altp2m is only supported with HAP\n");
>>> +        return -EINVAL;
>>> +    }
>>
>> Should this last one perhaps be further extended to permit altp2m with EPT
>> only?
> 
> Hm, yes, that would be more accurate as:
> 
> if ( altp2m_mode && (!hap || !hvm_altp2m_supported()) )

Wouldn't

   if ( altp2m_mode && !hvm_altp2m_supported() )

suffice? hvm_funcs.caps.altp2m is not supposed to be set when no HAP,
as long as HAP continues to be a pre-condition?

> Would you be fine adjusting at commit, or would you prefer me to send
> an updated version?

I'd be happy to fold in whatever we settle on.

Jan