On Fri, Feb 28, 2014 at 08:15:11AM -0800, H. Peter Anvin wrote: > On 02/28/2014 07:40 AM, Peter Zijlstra wrote: > > On Fri, Feb 28, 2014 at 07:13:06AM -0800, H. Peter Anvin wrote: > >> If I'm reading this right we end up going from the page fault > >> tracepoint to copy_from_user_nmi() without going through NMI, and the > >> cr2 corruption is obvious. I guess the assumption that only the NMI > >> path needed to save cr2 is flawed? > > > > It was never assumed it would only go through NMI, but that it would be > > NMI safe -- and as it turns out, it is that. > > > > What I did assume was that any other callsites would be safe, seeing how > > they'd already be running in 'normal' contexts. > > > > I had not considered people putting tracepoints _that_ early in the > > exception paths. > > > > Note that there's more tracepoints there than the one mentioned. > > > > Well, I was talking about the assumption spelled out in the comment > above copy_from_user_nmi() which pretty much states "cr2 is safe because > cr2 is saved/restored in the NMI wrappers."
That is because we assumed NMI was the only thing that could interrupt a fault handler before it would read CR2. Never thinking someone would put a tracepoint there. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
