Re: [PATCH v7 05/26] x86/fpu/xstate: Introduce fpu_guest_cfg for guest FPU configuration

[Yang, Weijiang]

On 11/30/2023 1:08 AM, Edgecombe, Rick P wrote:
> On Wed, 2023-11-29 at 22:12 +0800, Yang, Weijiang wrote:
> > On 11/28/2023 10:58 PM, Edgecombe, Rick P wrote:
> > > On Fri, 2023-11-24 at 00:53 -0500, Yang Weijiang wrote:
> > > > +       /*
> > > > +        * Set guest's __user_state_size to
> > > > fpu_user_cfg.default_size
> > > > so that
> > > > +        * existing uAPIs can still work.
> > > > +        */
> > > > +       fpu->guest_perm.__user_state_size =
> > > > fpu_user_cfg.default_size;
> > > It seems like an appropriate value, but where does this come into
> > > play
> > > exactly for guest FPUs?
> > I don't see there's special usage of this field for vCPU in VMM
> > userspace(QEMU).
> > Maybe it's mainly for AMX resulted usespace fault handling? For vCPU
> > thread,
> > it's only  referenced when AMX is enabled via __xfd_enable_feature()
> > .
> In that case the "so that existing uAPIs can still work" comment seems
> misleading. Maybe "this doesn't come into play for guest FPUs, but set
> it to a reasonable value"?

Ah, I mistook it for uabi_size and added comments. Will reword it properly.
Thank you for bringing it up!