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

[Andy Lutomirski]

On Thu, Jul 4, 2019 at 1:03 PM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
> Despire the current efforts to read CR2 before tracing happens there
> still exist a number of possible holes:
>
>   idtentry page_fault             do_page_fault           has_error_code=1
>     call error_entry
>       TRACE_IRQS_OFF
>         call trace_hardirqs_off*
>           #PF // modifies CR2
>
>       CALL_enter_from_user_mode
>         __context_tracking_exit()
>           trace_user_exit(0)
>             #PF // modifies CR2
>
>     call do_page_fault
>       address = read_cr2(); /* whoopsie */
>
> And similar for i386.
>
> Fix it by pulling the CR2 read into the entry code, before any of that
> stuff gets a chance to run and ruin things.

Reviewed-by: Andy Lutomirski <luto@xxxxxxxxxx>

Subject to the discussion as to whether this is the right approach at all.