From: Andi Kleen <ak@linux.intel.com>
To: Sasha Levin <sashal@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Andy Lutomirski <luto@kernel.org>,
"Bae, Chang Seok" <chang.seok.bae@intel.com>,
"Metzger, Markus T" <markus.t.metzger@intel.com>,
"hpa@zytor.com" <hpa@zytor.com>, "bp@alien8.de" <bp@alien8.de>,
"Hansen, Dave" <dave.hansen@intel.com>,
"Luck, Tony" <tony.luck@intel.com>,
Pedro Alves <palves@redhat.com>, Simon Marchi <simark@simark.ca>,
"Shankar, Ravi V" <ravi.v.shankar@intel.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v9 00/17] Enable FSGSBASE instructions
Date: Tue, 21 Apr 2020 12:56:29 -0700 [thread overview]
Message-ID: <20200421195629.GE608746@tassilo.jf.intel.com> (raw)
In-Reply-To: <20200421160622.GJ1809@sasha-vm>
> Andi's point is that there is no known user it breaks, and the Intel
> folks did some digging into potential users who might be affected by
> this, including 'rr' brought up by Andy, and concluded that there won't
> be breakage as a result of this patchset:
>
> https://mail.mozilla.org/pipermail/rr-dev/2018-March/000616.html
>
> Sure, if you poke at it you could see a behavior change, but is there
> an actual user that will be affected by it? I suspect not.
Actually we don't know of any behavior changes caused by the kernel
with selectors.
The application can change itself of course, but only if it uses the
new instructions, which no current application does.
[This was different in the original patch kit long ago which could
change behavior on context switch for programs with out of sync selectors,
but this has been long fixed]
A debugger can also change behavior, but we're not aware of any case
that it would break.
For rr or criu we're also not aware of any case that could break.
I honestly don't know what else could be done in due diligence.
Also just to reiterate merging this would immediately shave off
hundreds of cycles in most context switches.
-Andi
next prev parent reply other threads:[~2020-04-21 19:56 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-04 18:15 Chang S. Bae
2019-10-04 18:15 ` [PATCH v9 01/17] x86/ptrace: Prevent ptrace from clearing the FS/GS selector Chang S. Bae
2019-10-04 18:15 ` [PATCH v9 02/17] selftests/x86/fsgsbase: Test GS selector on ptracer-induced GS base write Chang S. Bae
2019-10-04 18:15 ` [PATCH v9 03/17] x86/cpu: Add 'unsafe_fsgsbase' to enable CR4.FSGSBASE Chang S. Bae
2019-10-04 18:15 ` [PATCH v9 04/17] x86/entry/64: Clean up paranoid exit Chang S. Bae
2019-10-04 18:15 ` [PATCH v9 05/17] x86/entry/64: Switch CR3 before SWAPGS in paranoid entry Chang S. Bae
2019-10-04 18:15 ` [PATCH v9 06/17] x86/entry/64: Introduce the FIND_PERCPU_BASE macro Chang S. Bae
2019-10-04 18:15 ` [PATCH v9 07/17] x86/entry/64: Handle FSGSBASE enabled paranoid entry/exit Chang S. Bae
2019-10-04 18:16 ` [PATCH v9 08/17] x86/entry/64: Document GSBASE handling in the paranoid path Chang S. Bae
2019-10-04 18:16 ` [PATCH v9 09/17] x86/fsgsbase/64: Add intrinsics for FSGSBASE instructions Chang S. Bae
2019-10-04 18:16 ` [PATCH v9 10/17] x86/fsgsbase/64: Enable FSGSBASE instructions in helper functions Chang S. Bae
2019-10-04 18:16 ` [PATCH v9 11/17] x86/fsgsbase/64: Use FSGSBASE in switch_to() if available Chang S. Bae
2019-10-04 18:16 ` [PATCH v9 12/17] x86/fsgsbase/64: Use FSGSBASE instructions on thread copy and ptrace Chang S. Bae
2019-10-04 18:16 ` [PATCH v9 13/17] x86/speculation/swapgs: Check FSGSBASE in enabling SWAPGS mitigation Chang S. Bae
2019-10-04 18:16 ` [PATCH v9 14/17] selftests/x86/fsgsbase: Test ptracer-induced GS base write with FSGSBASE Chang S. Bae
2019-10-04 18:16 ` [PATCH v9 15/17] x86/fsgsbase/64: Enable FSGSBASE on 64bit by default and add a chicken bit Chang S. Bae
2019-10-04 18:16 ` [PATCH v9 16/17] x86/elf: Enumerate kernel FSGSBASE capability in AT_HWCAP2 Chang S. Bae
2019-10-04 18:16 ` [PATCH v9 17/17] Documentation/x86/64: Add documentation for GS/FS addressing mode Chang S. Bae
2019-10-04 22:54 ` Randy Dunlap
2019-11-15 18:29 ` [PATCH v9 00/17] Enable FSGSBASE instructions Thomas Gleixner
2019-11-15 19:12 ` Andi Kleen
2019-11-29 14:56 ` Metzger, Markus T
2019-11-29 16:51 ` Andy Lutomirski
2019-12-02 8:23 ` Metzger, Markus T
2019-12-04 20:20 ` Andy Lutomirski
2019-12-10 8:27 ` Metzger, Markus T
2020-02-24 18:02 ` Bae, Chang Seok
2020-04-13 20:03 ` Sasha Levin
2020-04-14 0:32 ` Andi Kleen
2020-04-17 13:30 ` Sasha Levin
2020-04-17 15:52 ` Andy Lutomirski
2020-04-20 14:13 ` Andi Kleen
2020-04-20 17:14 ` Thomas Gleixner
2020-04-21 16:06 ` Sasha Levin
2020-04-21 16:49 ` Andy Lutomirski
2020-04-21 20:02 ` Andi Kleen
2020-04-21 17:15 ` Bae, Chang Seok
2020-04-21 19:56 ` Andi Kleen [this message]
2020-04-21 20:21 ` Andy Lutomirski
2020-04-21 20:51 ` Sasha Levin
2020-04-22 23:00 ` Andy Lutomirski
2020-04-23 4:08 ` Sasha Levin
2020-04-25 22:39 ` Thomas Gleixner
2020-04-26 2:52 ` Sasha Levin
2020-04-26 10:04 ` Thomas Gleixner
2020-04-14 15:47 ` Bae, Chang Seok
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