[Xen-devel] Re: [PATCH] FPU LWP 5/8: add a mask option to xsave() and xrstor()

[Wei Huang <wei.huang2@xxxxxxx>]

Hi Jan,

That is a good point. So far there isn't a way to decide which bits are 
guarded by CR0.TS. I will bring it up to our design team. I guess LWP 
will the only exception for a long while. Is the first approach 
sufficient/acceptable to you for now?
#define XSTATE_LAZY (XSTATE_ALL & ~XSTATE_NONLAZY)

Thanks,
-Wei


On 05/04/2011 02:02 AM, Jan Beulich wrote:
> > > > On 03.05.11 at 22:17, Wei Huang<wei.huang2@xxxxxxx>  wrote:
> > +#define XSTATE_LAZY    (XSTATE_FP | XSTATE_SSE | XSTATE_YMM)
> > +#define XSTATE_NONLAZY (XSTATE_LWP)
> > +#define XSTATE_ALL     (~0)
> As said before, this isn't forward compatible. New bits added in
> future hardware should explicitly *not* require changes to the OS
> (or hypervisor in our case). If you're certain LWP will remain the
> only piece not controlled via CR0.TS, then you'll want
>
> #define XSTATE_LAZY    (XSTATE_ALL&  ~XSTATE_NONLAZY)
>
> If you aren't (and I'm afraid you can't), then you'll have to ask
> your hardware guys to provide a means to detect which of the
> bits cover state not controlled by CR0.TS, and set these masks
> dynamically.
>
> Jan


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