From: Andy Lutomirski <luto@amacapital.net>
To: Ingo Molnar <mingo@kernel.org>
Cc: "Denys Vlasenko" <dvlasenk@redhat.com>,
"Kees Cook" <keescook@chromium.org>,
"Borislav Petkov" <bp@alien8.de>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"Oleg Nesterov" <oleg@redhat.com>,
"Denys Vlasenko" <vda.linux@googlemail.com>,
"Brian Gerst" <brgerst@gmail.com>,
"Frédéric Weisbecker" <fweisbec@gmail.com>,
"X86 ML" <x86@kernel.org>,
"Linus Torvalds" <torvalds@linux-foundation.org>,
"Rik van Riel" <riel@redhat.com>
Subject: Re: [RFC/INCOMPLETE 00/13] x86: Rewrite exit-to-userspace code
Date: Wed, 17 Jun 2015 08:16:41 -0700 [thread overview]
Message-ID: <CALCETrWEK7PyqSh3bWhkXH3J-CRgjyYUU5-YLNO0_1p5-wgGwg@mail.gmail.com> (raw)
In-Reply-To: <20150617094857.GB3940@gmail.com>
On Jun 17, 2015 2:49 AM, "Ingo Molnar" <mingo@kernel.org> wrote:
>
>
> * Andy Lutomirski <luto@kernel.org> wrote:
>
>
> > I tried to clean it up incrementally, but I decided it was too hard. Instead,
> > this series just replaces the code. It seems to work.
>
> Any known bugs beyond UML build breakage?
One minor one: the 64-bit and compat syscall asm changes should be
folded together. I was overly optimistic about bisectability -- the
intermediate step doesn't build. I haven't tested well enough to be
really comfortable with it, though.
There's another minor error in my description: the 32-bit code is not
a prerequisite for the exception_enter removal, so v2 will remove a
whole bunch of exception_enter calls. This considerably improves the
quality of the debugging checks.
>
> > Context tracking in particular works very differently now. The low-level entry
> > code checks that we're in CONTEXT_USER and switches to CONTEXT_KERNEL. The exit
> > code does the reverse. There is no need to track what CONTEXT_XYZ state we came
> > from, because we already know. Similarly, SCHEDULE_USER is gone, since we can
> > reschedule if needed by simply calling schedule() from C code.
> >
> > The main things that are missing are that I haven't done the 32-bit parts
> > (anyone want to help?) and therefore I haven't deleted the old C code. I also
> > think this may break UML for trivial reasons.
> >
> > Because I haven't converted the 32-bit code yet, all of the now-unnecessary
> > unnecessary calls to exception_enter are still present in traps.c.
> >
> > IRQ context tracking is still duplicated. We should probably clean it up by
> > changing the core code to supply something like
> > irq_enter_we_are_already_in_context_kernel.
> >
> > Thoughts?
>
> 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?
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...
--Andy
next prev parent reply other threads:[~2015-06-17 15:17 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-16 20:16 [RFC/INCOMPLETE 00/13] x86: Rewrite exit-to-userspace code Andy Lutomirski
2015-06-16 20:16 ` [RFC/INCOMPLETE 01/13] context_tracking: Add context_tracking_assert_state Andy Lutomirski
2015-06-17 9:41 ` Ingo Molnar
2015-06-17 14:15 ` Andy Lutomirski
2015-06-18 9:57 ` Ingo Molnar
2015-06-18 11:07 ` Andy Lutomirski
2015-06-18 15:52 ` Andy Lutomirski
2015-06-18 16:17 ` Ingo Molnar
2015-06-18 16:26 ` Frederic Weisbecker
2015-06-18 19:26 ` Andy Lutomirski
2015-06-17 15:27 ` Paul E. McKenney
2015-06-18 9:59 ` Ingo Molnar
2015-06-18 22:54 ` Paul E. McKenney
2015-06-19 2:19 ` Paul E. McKenney
2015-06-30 11:04 ` Ingo Molnar
2015-06-30 16:16 ` Paul E. McKenney
2015-06-16 20:16 ` [RFC/INCOMPLETE 02/13] notifiers: Assert that RCU is watching in notify_die Andy Lutomirski
2015-06-16 20:16 ` [RFC/INCOMPLETE 03/13] x86: Move C entry and exit code to arch/x86/entry/common.c Andy Lutomirski
2015-06-16 20:16 ` [RFC/INCOMPLETE 04/13] x86/traps: Assert that we're in CONTEXT_KERNEL in exception entries Andy Lutomirski
2015-06-16 20:16 ` [RFC/INCOMPLETE 05/13] x86/entry: Add enter_from_user_mode and use it in syscalls Andy Lutomirski
2015-06-16 20:16 ` [RFC/INCOMPLETE 06/13] x86/entry: Add new, comprehensible entry and exit hooks Andy Lutomirski
2015-06-16 20:16 ` [RFC/INCOMPLETE 07/13] x86/entry/64: Really create an error-entry-from-usermode code path Andy Lutomirski
2015-06-16 20:16 ` [RFC/INCOMPLETE 08/13] x86/entry/64: Migrate 64-bit syscalls to new exit hooks Andy Lutomirski
2015-06-17 10:00 ` Ingo Molnar
2015-06-17 10:02 ` Ingo Molnar
2015-06-17 14:12 ` Andy Lutomirski
2015-06-18 10:17 ` Ingo Molnar
2015-06-18 10:19 ` Ingo Molnar
2015-06-16 20:16 ` [RFC/INCOMPLETE 09/13] x86/entry/compat: Migrate compat " Andy Lutomirski
2015-06-16 20:16 ` [RFC/INCOMPLETE 10/13] x86/asm/entry/64: Save all regs on interrupt entry Andy Lutomirski
2015-06-16 20:16 ` [RFC/INCOMPLETE 11/13] x86/asm/entry/64: Simplify irq stack pt_regs handling Andy Lutomirski
2015-06-16 20:16 ` [RFC/INCOMPLETE 12/13] x86/asm/entry/64: Migrate error and interrupt exit work to C Andy Lutomirski
2015-06-16 20:16 ` [RFC/INCOMPLETE 13/13] x86/entry: Remove SCHEDULE_USER and asm/context-tracking.h Andy Lutomirski
2015-06-17 9:48 ` [RFC/INCOMPLETE 00/13] x86: Rewrite exit-to-userspace code Ingo Molnar
2015-06-17 10:13 ` Richard Weinberger
2015-06-17 11:04 ` Ingo Molnar
2015-06-17 14:19 ` Andy Lutomirski
2015-06-17 15:16 ` Andy Lutomirski [this message]
2015-06-18 10:14 ` Ingo Molnar
2015-06-17 10:32 ` Ingo Molnar
2015-06-17 11:14 ` Ingo Molnar
2015-06-17 14:23 ` Andy Lutomirski
2015-06-18 10:11 ` Ingo Molnar
2015-06-18 11:06 ` Andy Lutomirski
2015-06-18 16:24 ` Ingo Molnar
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