lkml.org 
[lkml]   [2015]   [Jul]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: Dealing with the NMI mess
On Thu, Jul 23, 2015 at 01:38:33PM -0700, Linus Torvalds wrote:
> On Thu, Jul 23, 2015 at 1:21 PM, Andy Lutomirski <luto@amacapital.net> wrote:
> >
> > 2. Forbid IRET inside NMIs. Doable but maybe not that pretty.
> >
> > We haven't considered:
> >
> > 3. Forbid faults (other than MCE) inside NMI.
>
> I'd really prefer #2. #3 depends on us getting many things right, and
> never introducing new cases in the future.
>
> #2, in contrast, seems to be fairly localized. Yes, RF is an issue,
> but returning to user space with RF clear doesn't really seem to be
> all that problematic.

What's the worst case that can happen with RF cleared when returing
to user space ? My understanding is that it's just that we risk to
break again on an instruction that had a break point set and which
already triggered the breakpoint, right ?

If so the problem probably is whether there's a risk of looping again
without ever getting a chance to execute this instruction normally.
But if the NMIs don't bomb as fast as we can process them, at some
point the instruction should get a chance to be executed, so the
problem doesn't seem dramatic.

That makes me think that I have no idea what happens if we try to
step-trace "int 2", I don't even know if we pass through the NMI
handler.

Willy



\
 
 \ /
  Last update: 2015-07-23 23:01    [W:0.133 / U:2.040 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site