Re: [PATCH v2 5/7] x86/mm, tracing: Fix CR2 corruption

[Andy Lutomirski]

> On Jul 4, 2019, at 7:18 PM, Linus Torvalds <torva...@linux-foundation.org> 
> wrote:
> 
>> On Fri, Jul 5, 2019 at 5:03 AM Peter Zijlstra <pet...@infradead.org> wrote:
>> 
>> Despire the current efforts to read CR2 before tracing happens there
>> still exist a number of possible holes:
> 
> So this whole series disturbs me for the simple reason that I thought
> tracing was supposed to save/restore cr2 and make it unnecessary to
> worry about this in non-tracing code.
> 
> That is very much what the NMI code explicitly does. Why shouldn't all
> the other tracing code do the same thing in case they can take page
> faults?
> 

If nothing else, MOV to CR2 is architecturally serializing, so, unless there’s 
some fancy unwinding involved, this will be quite slow.