Runtime check for PAE option on BSD 6+ i386

[John Baldwin]

On Tuesday, May 03, 2011 1:43:39 pm Kostik Belousov wrote:
> On Tue, May 03, 2011 at 11:44:32AM -0400, John Baldwin wrote:
> > On Tuesday, May 03, 2011 9:10:26 am Philip Soeberg wrote:
> > > Hi fellow FreeBSD hackers,
> > > 
> > > I've been using the following poor-man's approach in my driver init for 
> > > ages in an attempt at detecting PAE option on BSD 6 (or greater) i386 
> > > kernels, as I depend on dmabus(9) but provide a loadable kernel module only.
> > > 
> > >  >>>
> > >    if (sizeof(void*) == 4) {
> > >      if (((uint64_t)(cnt.v_page_count * cnt.v_page_size) / 1073741824) 
> > >  >= 4) {
> > >        printf("FreeBSD i386 detected with PAE option enabled. FreeBSD 
> > > PAE type\n");
> > >        printf("kernels does not support loadable modules which use DMA. 
> > > Please\n");
> > >        printf("reconfigure your kernel for non-PAE or switch to amd64 
> > > kernel.\n");
> > >        return EFAULT;
> > >      }
> > >    }
> > > <<<
> > 
> > Hmmm, even this isn't really accurate as some folks may choose to enable PAE
> > even with < 4GB to get PG_NX functionality.
> >  
> > > afaik there's a sysctl method of checking this per BSD7 (or is it 8?), 
> > > but what about BSD6? Any hints on how I can runtime detect the above?
> > 
> > Definitely a kern.features.pae sysctl in 7.  I don't see anything similar in 
> > 6.  
> 
> Read %cr4 and test the bit there.

Oh, cute. :)

-- 
John Baldwin