PERFORCE change 75366 for review

[John Baldwin]

On Tuesday 26 April 2005 09:36 am, David Xu wrote:
> John Baldwin wrote:
> > On Apr 17, 2005, at 6:42 AM, David Xu wrote:
> >> http://perforce.freebsd.org/chv.cgi?CH=75366
> >>
> >> Change 75366 by davidxu at davidxu_alona on 2005/04/17 10:42:05
> >>
> >>     Implement cpu_set_user_tls for sparc64.
> >>
> >> Affected files ...
> >>
> >> ..
> >> //depot/projects/davidxu_thread/src/sys/sparc64/sparc64/vm_machdep.c#6
> >> edit
> >>
> >> Differences ...
> >>
> >> ====
> >> //depot/projects/davidxu_thread/src/sys/sparc64/sparc64/vm_machdep.c#6
> >> (text+ko) ====
> >>
> >> @@ -194,6 +194,15 @@
> >>      td->td_retval[1] = tf->tf_out[1];
> >>  }
> >>
> >> +void
> >> +cpu_set_user_tls(struct thread *td, void *tls_base, size_t tls_size,
> >> +        int tls_seg __unused)
> >> +{
> >> +    if (td == curthread)
> >> +        flushw();
> >> +    td->td_frame->tf_global[7] = tls_base;
> >> +}
> >> +
> >
> > I think for at least this one and Alpha you might want a critical
> > section in the curthread case like you do on i386 and amd64 since
> > calling the Alpha PAL and setting tls_base + flushw() are more than
> > one instruction long.
>
> If this is true, why don't set_mcontext on sparc64 and alpha enter
> critical region ?

Bugs. :)  Actually, sparc64 is probably ok, but alpha_pal_wrunique() on Alpha 
is basically the same as wrmsr() on x86.  You might be ok without a critical 
section on Alpha but I'm not sure.  Actually, I think you are fine.  The 
thread can't get out into userland without resuming and finishing this 
function first.

> I enter critical region on i386 and amd64, because I have to write
> global register (amd64 MSR) or gdt on i386, if thread is preempted,
> then it may be in intermediate state, for example on amd64:
>          td->td_pcb->pcb_fsbase = (register_t)tls_base;
> --->
>          wrmsr(MSR_FSBASE, td->td_pcb->pcb_fsbase);
>
> if thread is preempted at ---->, a rdmsr in cpu_switch() will overwrite
> the value I set before I can write it into MSR_FSBASE register.
>
> David Xu

-- 
John Baldwin <jhb at FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve"  =  http://www.FreeBSD.org