Re: [PATCH 2/5] x86, mpx: hook #BR exception handler to allocatebound tables
From: Steven Rostedt
Date: Fri Jan 17 2014 - 12:11:05 EST
On Fri, 17 Jan 2014 17:47:36 +0100
Borislav Petkov <bp@xxxxxxxxx> wrote:
> On Fri, Jan 17, 2014 at 02:47:15PM +0000, Ren, Qiaowei wrote:
> > > do_bounds
> > > |->do_mpx_bt_fault
> > > |->allocate_bt
> > > |->sys_mmap_pgoff
> > > |->vm_mmap_pgoff
> > > |->do_mmap_pgoff
> > > |->mmap_region
> > > |-> kmem_cache_zalloc(vm_area_cachep, GFP_KERNEL);
> > >
> > Sorry for my late reply.
> > Petkov, could you please detail the problem? Memory allocation can't
> > be done in the eception handler? I guess it is like do_page_fault(),
> > right?
> Right, so Steve and I played a couple of scenarios in IRC with this. So
> #BR is comparable with #PF, AFAICT, and as expected we don't take any
> locks when handling page faults in kernel space as we might deadlock.
> Now, what happens if a thread is sleeping on some lock down that
> GFP_KERNEL allocation path and another thread gets a #BR and goes that
> same mmap_pgoff path and tries to grab that same lock?
> Also, what happens if you take a #BR in NMI context, say the NMI
> All I'm trying to say is, it might not be such a good idea to sleep in a
> fault handler...
Or do what #PF does. Check if the fault happened in the kernel and go
one path (probably follow what do_fault() does), otherwise if it is
userspace, it's ok to sleep or grab locks or whatever you want.
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/