Messages in this thread | | | Date | Fri, 17 Jan 2014 08:51:03 -0800 | From | "H. Peter Anvin" <> | Subject | Re: [PATCH 2/5] x86, mpx: hook #BR exception handler to allocate bound tables |
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On 01/17/2014 08:47 AM, Borislav Petkov wrote: > > 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?
It goes to sleep. Same as if we take a page fault and have to page something in.
> Also, what happens if you take a #BR in NMI context, say the NMI > handler?
You should never, ever do that. We should never take a #BR in the kernel, full stop -- if we do it is panic time.
> All I'm trying to say is, it might not be such a good idea to sleep in a > fault handler...
A fault handler from user space is really nothing other than a different kind of system call. It is nothing magic about it.
-hpa
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