svn commit: r217587 - head/sys/i386/i386

[Jung-uk Kim]

On Wednesday 19 January 2011 12:18 pm, Kostik Belousov wrote:
> On Wed, Jan 19, 2011 at 05:09:07PM +0000, Jung-uk Kim wrote:
> > Author: jkim
> > Date: Wed Jan 19 17:09:07 2011
> > New Revision: 217587
> > URL: http://svn.freebsd.org/changeset/base/217587
> >
> > Log:
> >   Fix yet another fallout from r208833.  VM86 BIOS call may cause
> > page fault when FPU is in use.
> >
> >   Reported by:	Marc UBM Bocklet (ubm dot freebsd at googlemail
> > dot com) Tested by:	b. f. (bf1783 at googlemail dot com)
> >   MFC after:	3 days
> >
> > Modified:
> >   head/sys/i386/i386/vm86bios.s
> >
> > Modified: head/sys/i386/i386/vm86bios.s
> > =================================================================
> >============= --- head/sys/i386/i386/vm86bios.s	Wed Jan 19
> > 17:04:07 2011	(r217586) +++ head/sys/i386/i386/vm86bios.s	Wed Jan
> > 19 17:09:07 2011	(r217587) @@ -73,10 +73,9 @@
> > ENTRY(vm86_bioscall)
> >  	je 	1f			/* no curproc/npxproc */
> >  	pushl	%edx
> >  	movl	TD_PCB(%ecx),%ecx
> > -	addl	$PCB_SAVEFPU,%ecx
> > -	pushl	%ecx
> > +	pushl	PCB_SAVEFPU(%ecx)
> >  	call	npxsave
> > -	popl	%ecx
> > +	addl	$4,%esp
> >  	popl	%edx			/* recover our pcb */
> >  1:
> >  	popfl
>
> vm86_bioscall() in fact inlines the old version of npxexit().
> Shouldn't the npxexit() be called from C code before call to
> vm86_bioscall ?

I think we can but I don't like redundant or nested uses of 
critical_enter()/critical_exit() from vm86_intcall()/vm86_datacall().  
And I don't think that's worth the code churn.

> Also, if bioscall can be used from the syscall context, I think
> whatever npxsave()/npxexit() is used, and BIOS modifies FPU
> state, we are corrupting usermode FPU context.
>
> Probably, fpu_kern_enter()/fpu_kern_leave() braces around
> vm86_bioscall is proper solution.

BIOS should never modify FPU state, AFAIK.

Jung-uk Kim