Re: [PATCH 4/8] x86/fpu: Remove the thread::fpu pointer

[Peter Zijlstra]

On Thu, Apr 10, 2025 at 12:10:56PM +0200, Ingo Molnar wrote:
> 
> * Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> 
> > On Wed, Apr 09, 2025 at 11:11:23PM +0200, Ingo Molnar wrote:
> > 
> > > diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
> > > index 5ea7e5d2c4de..b7f7c9c83409 100644
> > > --- a/arch/x86/include/asm/processor.h
> > > +++ b/arch/x86/include/asm/processor.h
> > > @@ -514,12 +514,9 @@ struct thread_struct {
> > >  
> > >  	struct thread_shstk	shstk;
> > >  #endif
> > > -
> > > -	/* Floating point and extended processor state */
> > > -	struct fpu		*fpu;
> > >  };
> > >  
> > > -#define x86_task_fpu(task) ((task)->thread.fpu)
> > > +#define x86_task_fpu(task)	((struct fpu *)((void *)(task) + sizeof(*(task))))
> > 
> > Doesn't our FPU state need to be cacheline aligned?
> 
> Yeah, and we do have a check for that:
> 
> +       BUILD_BUG_ON(sizeof(*dst) % SMP_CACHE_BYTES != 0);

Ah, missed that. Clearly I need to improve my reading skillz :-)