Re: [RFC/INCOMPLETE 00/13] x86: Rewrite exit-to-userspace code

From: Ingo Molnar
Date: Thu Jun 18 2015 - 06:15:02 EST

* Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:

> > So assuming you fix the UML build I'm inclined to go for it, even in this
> > incomplete form, to increase testing coverage.
> >
> > Doing that will also decrease ongoing merge friction between your work and
> > other entry code cleanups ...
> Sounds good to me. I'm not convinced this is 4.2 material, though. Would it go
> in a separate branch for now?

Please send it out as a separate series, on top of -tip, I'll probably stick it
into a separate branch for the time being.

> On a related note, do you have any idea what work_notifysig_v86 in entry_32.S is
> for? It seems unnecessary and wrong to me. Unnecessary because we have
> return_to_32bit. Wrong because I don't see how we can reliably enter vm86 mode
> if we have exit work enabled -- one of the giant turds in vm86_32.c literally
> jumps from C code to resume_userspace on vm86 entry, and resume_userspace
> promptly checks for work and might land in work_notifysig_v86 before we ever
> make it to v8086/user mode.
> I think it may actually be impossible to use vm86 under ptrace. ISTR I had some
> trouble when trying to strace my test case...

Should be tested really, I'm all for removing it if simple vm86 mode games
continue to work ;-)


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