Messages in this thread | | | Date | Fri, 17 Jan 2014 12:10:54 -0500 | From | Steven Rostedt <> | Subject | Re: [PATCH 2/5] x86, mpx: hook #BR exception handler to allocate bound tables |
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On Fri, 17 Jan 2014 17:47:36 +0100 Borislav Petkov <bp@alien8.de> 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 > handler? > > 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.
-- Steve
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