From: Thomas Gleixner <tglx@linutronix.de>
To: Arvind Sankar <nivedita@alum.mit.edu>
Cc: Arvind Sankar <nivedita@alum.mit.edu>,
"Paul E. McKenney" <paulmck@kernel.org>,
Nick Desaulniers <ndesaulniers@google.com>,
Ingo Molnar <mingo@redhat.com>, Arnd Bergmann <arnd@arndb.de>,
Borislav Petkov <bp@alien8.de>,
"maintainer\:X86 ARCHITECTURE \(32-BIT AND 64-BIT\)"
<x86@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Zhenzhong Duan <zhenzhong.duan@oracle.com>,
Kees Cook <keescook@chromium.org>,
Peter Zijlstra <peterz@infradead.org>,
Juergen Gross <jgross@suse.com>,
Andy Lutomirski <luto@kernel.org>,
Andrew Cooper <andrew.cooper3@citrix.com>,
LKML <linux-kernel@vger.kernel.org>,
clang-built-linux <clang-built-linux@googlegroups.com>,
Will Deacon <will@kernel.org>,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH] x86: work around clang IAS bug referencing __force_order
Date: Fri, 21 Aug 2020 02:37:48 +0200 [thread overview]
Message-ID: <87zh6ohm03.fsf@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20200820130641.GA536306@rani.riverdale.lan>
On Thu, Aug 20 2020 at 09:06, Arvind Sankar wrote:
> I don't think that's an issue, or at least, not one where force_order
> helps.
>
> If the source for foo() is not visible to the compiler, the only reason
> force_order prevents the reordering is because foo() might have
> references to it, but equally foo() might have volatile asm, so the
> reordering isn't possible anyway.
>
> If the source is visible, force_order won't prevent any reordering
> except across references to force_order, but the only references are
> from the volatile asm's which already prevent reordering.
>
> I think force_order can only help with buggy compilers, and for those it
> should really have been an input-output operand -- it wouldn't currently
> do anything to prevent cr writes from being reordered.
Fair enough. Care to provide a patch which has the collected wisdom of
this thread in the changelog?
Thanks,
tglx
next prev parent reply other threads:[~2020-08-21 0:37 UTC|newest]
Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-27 13:53 [PATCH] x86: work around clang IAS bug referencing __force_order Arnd Bergmann
2020-08-01 11:50 ` Sedat Dilek
2020-08-06 22:13 ` Thomas Gleixner
2020-08-07 7:03 ` Sedat Dilek
2020-08-04 0:09 ` Nick Desaulniers
2020-08-14 17:29 ` Sedat Dilek
2020-08-14 21:19 ` Sedat Dilek
2020-08-14 22:57 ` Nick Desaulniers
2020-08-15 0:26 ` Nick Desaulniers
2020-08-15 3:28 ` Sedat Dilek
2020-08-15 8:23 ` Sedat Dilek
2020-08-15 10:46 ` Sedat Dilek
2020-08-15 14:39 ` Sedat Dilek
2020-08-16 9:37 ` Sedat Dilek
2020-08-06 22:11 ` Thomas Gleixner
2020-08-13 0:12 ` Nick Desaulniers
2020-08-13 8:49 ` David Laight
2020-08-13 17:20 ` Arvind Sankar
2020-08-13 17:28 ` Thomas Gleixner
2020-08-13 17:37 ` Paul E. McKenney
2020-08-13 18:09 ` Arvind Sankar
2020-08-13 18:20 ` Paul E. McKenney
2020-08-20 10:44 ` Thomas Gleixner
2020-08-20 13:06 ` Arvind Sankar
2020-08-21 0:37 ` Thomas Gleixner [this message]
2020-08-21 23:04 ` Arvind Sankar
2020-08-21 23:16 ` Nick Desaulniers
2020-08-21 23:25 ` Arvind Sankar
2020-08-22 0:43 ` Thomas Gleixner
2020-08-22 3:55 ` Arvind Sankar
2020-08-22 8:41 ` Segher Boessenkool
2020-08-22 9:23 ` Sedat Dilek
2020-08-22 9:51 ` Sedat Dilek
2020-08-22 10:26 ` Segher Boessenkool
2020-08-22 10:35 ` Arnd Bergmann
2020-08-22 18:17 ` Miguel Ojeda
2020-08-22 21:08 ` Linus Torvalds
2020-08-22 23:10 ` Arvind Sankar
2020-08-23 0:10 ` Linus Torvalds
2020-08-23 1:16 ` Arvind Sankar
2020-08-23 21:25 ` [PATCH] x86/asm: Replace __force_order with memory clobber Arvind Sankar
2020-08-24 17:50 ` Nathan Chancellor
2020-08-24 19:13 ` Miguel Ojeda
2020-08-25 15:19 ` Arvind Sankar
2020-08-25 15:21 ` Sedat Dilek
2020-09-02 15:33 ` [PATCH v2] " Arvind Sankar
2020-09-02 15:58 ` David Laight
2020-09-02 16:14 ` Arvind Sankar
2020-09-02 16:08 ` Arvind Sankar
2020-09-02 20:26 ` David Laight
2020-09-02 17:16 ` Segher Boessenkool
2020-09-02 17:36 ` Arvind Sankar
2020-09-02 18:19 ` Miguel Ojeda
2020-09-02 18:24 ` Arvind Sankar
2020-09-02 23:21 ` [PATCH v3] " Arvind Sankar
2020-09-03 2:17 ` Kees Cook
2020-09-03 5:34 ` Miguel Ojeda
2020-09-30 20:50 ` Kees Cook
2020-10-01 10:12 ` [tip: x86/asm] x86/asm: Replace __force_order with a " tip-bot2 for Arvind Sankar
2020-10-13 9:30 ` tip-bot2 for Arvind Sankar
2020-08-22 21:17 ` [PATCH] x86: work around clang IAS bug referencing __force_order Arvind Sankar
2020-08-23 13:31 ` David Laight
2020-09-08 22:25 ` Pavel Machek
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=87zh6ohm03.fsf@nanos.tec.linutronix.de \
--to=tglx@linutronix.de \
--cc=andrew.cooper3@citrix.com \
--cc=arnd@arndb.de \
--cc=bp@alien8.de \
--cc=clang-built-linux@googlegroups.com \
--cc=hpa@zytor.com \
--cc=jgross@suse.com \
--cc=keescook@chromium.org \
--cc=kirill.shutemov@linux.intel.com \
--cc=linux-kernel@vger.kernel.org \
--cc=luto@kernel.org \
--cc=mingo@redhat.com \
--cc=ndesaulniers@google.com \
--cc=nivedita@alum.mit.edu \
--cc=paulmck@kernel.org \
--cc=peterz@infradead.org \
--cc=torvalds@linux-foundation.org \
--cc=will@kernel.org \
--cc=x86@kernel.org \
--cc=zhenzhong.duan@oracle.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.