linux-kernel - Re: [PATCH 23/30] x86, kaiser: use PCID feature to make user and kernel switches faster

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <157fa017-16d8-af5b-f6c3-77794c0546cf@linux.intel.com>
Date:   Thu, 16 Nov 2017 11:25:10 -0800
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Andrea Arcangeli <aarcange@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        moritz.lipp@...k.tugraz.at, daniel.gruss@...k.tugraz.at,
        michael.schwarz@...k.tugraz.at, richard.fellner@...dent.tugraz.at,
        luto@...nel.org, torvalds@...ux-foundation.org,
        keescook@...gle.com, hughd@...gle.com, x86@...nel.org
Subject: Re: [PATCH 23/30] x86, kaiser: use PCID feature to make user and
 kernel switches faster

On 11/16/2017 11:19 AM, Andrea Arcangeli wrote:
> On Fri, Nov 10, 2017 at 11:31:50AM -0800, Dave Hansen wrote:
>> Hugh Dickins also points out that PCIDs really have two distinct
>> use-cases in the context of KAISER.  The first way they can be used
> I don't see why you try to retain such a minor optimization for newer
> Intel chips when at the same you prevent KAISER to run with good
> performance on older Intel chips like SandyBridge/IvyBridge which
> would create a major performance regression for those two.

This was more straightforward to do.

The other way requires having *TWO* PCID modes.  So, we need to
disambiguate the two modes in the existing infrastructure in addition to
adding KAISER.

Had I gone and done that, my fear was that we would be left with no
usable PCIDs on *any* hardware.  So, this was easier, I went and did it
first, and I'd love to see someone add support for PCIDs on those older
non-INVPCID systems.  "Someone" may even be me, but it'll be in v2.

Patches welcome before then. :)