linux-kernel - Re: [patch RFC 00/15] mm/highmem: Provide a preemptible variant of kmap

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: <20200923101953.GT2674@hirez.programming.kicks-ass.net>
Date:   Wed, 23 Sep 2020 12:19:53 +0200
From:   peterz@...radead.org
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Paul McKenney <paulmck@...nel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Will Deacon <will@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux-MM <linux-mm@...ck.org>,
        Russell King <linux@...linux.org.uk>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Chris Zankel <chris@...kel.net>,
        Max Filippov <jcmvbkbc@...il.com>,
        linux-xtensa@...ux-xtensa.org,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        intel-gfx <intel-gfx@...ts.freedesktop.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Vineet Gupta <vgupta@...opsys.com>,
        "open list\:SYNOPSYS ARC ARCHITECTURE" 
        <linux-snps-arc@...ts.infradead.org>,
        Arnd Bergmann <arnd@...db.de>, Guo Ren <guoren@...nel.org>,
        linux-csky@...r.kernel.org, Michal Simek <monstr@...str.eu>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        linux-mips@...r.kernel.org, Nick Hu <nickhu@...estech.com>,
        Greentime Hu <green.hu@...il.com>,
        Vincent Chen <deanbo422@...il.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        "David S. Miller" <davem@...emloft.net>,
        linux-sparc <sparclinux@...r.kernel.org>
Subject: Re: [patch RFC 00/15] mm/highmem: Provide a preemptible variant of
 kmap_atomic & friends

On Mon, Sep 21, 2020 at 09:27:57PM +0200, Thomas Gleixner wrote:
> Alternatively this could of course be solved with per CPU page tables
> which will come around some day anyway I fear.

Previously (with PTI) we looked at making the entire kernel map per-CPU,
and that takes a 2K copy on switch_mm() (or more general, the user part
of whatever the top level directory is for architectures that have a
shared kernel/user page-table setup in the first place).

The idea was having a fixed per-cpu kernel page-table, share a bunch of
(kernel) page-tables between all CPUs and then copy in the user part on
switch.

I've forgotten what the plan was for ASID/PCID in that scheme.

For x86_64 we've been fearing the performance of that 2k copy, but I
don't think we've ever actually bit the bullet and implemented it to see
how bad it really is.