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Message-ID: <CA+55aFwJ1=pyr9fP_UzDjnyX2qJ4mpxg_DTTiOJTv9PFW4dHgg@mail.gmail.com>
Date: Fri, 24 Jun 2016 10:21:50 -0700
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Brian Gerst <brgerst@...il.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Oleg Nesterov <oleg@...hat.com>,
Andy Lutomirski <luto@...capital.net>, Andy Lutomirski <luto@...nel.org>,
"the arch/x86 maintainers" <x86@...nel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>, Borislav Petkov <bp@...en8.de>,
Nadav Amit <nadav.amit@...il.com>, Kees Cook <keescook@...omium.org>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, Josh Poimboeuf <jpoimboe@...hat.com>,
Jann Horn <jann@...jh.net>, Heiko Carstens <heiko.carstens@...ibm.com>
Subject: Re: [PATCH v3 00/13] Virtually mapped stacks with guard pages (x86, core)
On Fri, Jun 24, 2016 at 5:25 AM, Brian Gerst <brgerst@...il.com> wrote:
> *
> * rdi: prev task we switched from
> + * rsi: task we're switching to
> */
> ENTRY(ret_from_fork)
> - LOCK ; btr $TIF_FORK, TI_flags(%r8)
> + LOCK ; btr $TIF_FORK, TI_flags(%rsi) /* rsi: this newly forked task */
>
> call schedule_tail /* rdi: 'prev' task parameter */
>
> I think you forgot GET_THREAD_INFO() here. RSI is the task, not the
> thread_info. FYI, this goes away with my switch_to() rewrite, which
> removes TIF_FORK.
The point of that patch series is to make the thread_info and the
task_struct pointer have the same value on x86 - we hide the
thread_info inside the task_struct itself, and in fact at the
beginning of it.
That allows for the above kinds of simplification - use the task
struct pointer and thread info interchangably in the asm code.
But as mentioned, I must have missed something. There were a number of
places where the code used the task_stack_page() and
task_thread_info() interchangably, which used to work and is no longer
true. There might simply be cases I missed.
Or there might simply be cases I screwed up.
Linus
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