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

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

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@xxxxxxxx> 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.

Roger.

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