Re: [Xen-devel] [PATCH v1] x86/altp2m: Add hypercall to create a new view and set sve bits

From: Alexandru Stefan ISAILA <aisaila@bitdefender.com>
To: "Roger Pau Monné" <roger.pau@citrix.com>
Cc: "kevin.tian@intel.com" <kevin.tian@intel.com>,
	"sstabellini@kernel.org" <sstabellini@kernel.org>,
	Jan Beulich <jbeulich@suse.com>, "wl@xen.org" <wl@xen.org>,
	"konrad.wilk@oracle.com" <konrad.wilk@oracle.com>,
	"george.dunlap@eu.citrix.com" <george.dunlap@eu.citrix.com>,
	Tamas K Lengyel <tamas.k.lengyel@gmail.com>,
	"ian.jackson@eu.citrix.com" <ian.jackson@eu.citrix.com>,
	"tim@xen.org" <tim@xen.org>,
	"julien.grall@arm.com" <julien.grall@arm.com>,
	"jun.nakajima@intel.com" <jun.nakajima@intel.com>,
	"andrew.cooper3@citrix.com" <andrew.cooper3@citrix.com>,
	"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
Subject: Re: [Xen-devel] [PATCH v1] x86/altp2m: Add hypercall to create a new view and set sve bits
Date: Fri, 25 Oct 2019 14:40:36 +0000	[thread overview]
Message-ID: <6b546dcd-779b-d3cb-6602-d2fee2c66fd9@bitdefender.com> (raw)
In-Reply-To: <050b1ecd-8c3e-ae4a-60a9-f9b36340f749@bitdefender.com>


On 25.10.2019 17:36, Alexandru Stefan ISAILA wrote:
> 
> 
> On 23.10.2019 14:58, Roger Pau Monné wrote:
>> On Wed, Oct 23, 2019 at 09:11:54AM +0000, Alexandru Stefan ISAILA wrote:
>>>
>>>
>>> On 03.09.2019 20:24, Tamas K Lengyel wrote:
>>>> On Tue, Sep 3, 2019 at 9:53 AM Jan Beulich <jbeulich@suse.com> wrote:
>>>>>
>>>>> On 02.09.2019 10:11, Alexandru Stefan ISAILA wrote:
>>>>>> --- a/xen/include/public/hvm/hvm_op.h
>>>>>> +++ b/xen/include/public/hvm/hvm_op.h
>>>>>> @@ -244,6 +244,7 @@ struct xen_hvm_altp2m_view {
>>>>>>         /* Create view only: default access type
>>>>>>          * NOTE: currently ignored */
>>>>>>         uint16_t hvmmem_default_access; /* xenmem_access_t */
>>>>>> +    uint8_t set_sve; /* bool value */
>>>>>>     };
>>>>>
>>>>> This interface is, given the right configuration, available to
>>>>> guests. Hence you can't simply add a field here. Just consider
>>>>> what happens for an existing caller when there is random data
>>>>> in the field you now assign a meaning.
>>>>
>>>> Perhaps instead of extending the HVMOP it would make more sense to
>>>> just add a xl config option that defines the "default" sve bit for
>>>> altp2m views in the domain?
>>>>
>>>
>>> Adding a xl config option will not work for systems that do use xl.
>>> There is a need that this will work in all cases.
>>
>> I assume that such option would be implemented using a DOMCTL, which
>> can also be used by other toolstacks. I however have no idea whether
>> this is a suitable interface or not for this feature.
>>
> 
> I think that having a HVMOP_altp2m_get_suppress_ve_multi and letting the
HVMOP_altp2m_set_suppress_ve_multi (sorry for the typo)
> caller provide the start gfn and the nr of pages to have the sve bits
> set will provide a good solution for init an dfor further development.
> 
> I will go on this way for version 2 if everyone is ok with this.
> 
> Thanks,
> Alex
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