From: Martin Schwidefsky <schwidefsky@de.ibm.com>
To: Pavel Machek <pavel@ucw.cz>
Cc: linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org,
Heiko Carstens <heiko.carstens@de.ibm.com>,
Christian Borntraeger <borntraeger@de.ibm.com>,
Cornelia Huck <cohuck@redhat.com>,
David Hildenbrand <david@redhat.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Jon Masters <jcm@redhat.com>, Marcus Meissner <meissner@suse.de>,
Jiri Kosina <jkosina@suse.cz>,
Dominik Brodowski <linux@dominikbrodowski.net>,
Alan Cox <gnomes@lxorguk.ukuu.org.uk>,
David Woodhouse <dwmw2@infradead.org>
Subject: Re: [PATCH 6/6] s390: introduce execute-trampolines for branches
Date: Wed, 7 Feb 2018 12:51:48 +0100 [thread overview]
Message-ID: <20180207125148.2c657e58@mschwideX1> (raw)
In-Reply-To: <20180207100726.GB31392@amd>
On Wed, 7 Feb 2018 11:07:26 +0100
Pavel Machek <pavel@ucw.cz> wrote:
> On Wed 2018-02-07 08:00:11, Martin Schwidefsky wrote:
> > Add CONFIG_EXPOLINE to enable the use of the new -mindirect-branch= and
> > -mfunction_return= compiler options to create a kernel fortified against
> > the specte v2 attack.
> >
> > With CONFIG_EXPOLINE=y all indirect branches will be issued with an
> > execute type instruction. For z10 or newer the EXRL instruction will
> > be used, for older machines the EX instruction. The typical indirect
> > call
> >
> > basr %r14,%r1
> >
> > is replaced with a PC relative call to a new thunk
> >
> > brasl %r14,__s390x_indirect_jump_r1
> >
> > The thunk contains the EXRL/EX instruction to the indirect branch
> >
> > __s390x_indirect_jump_r1:
> > exrl 0,0f
> > j .
> > 0: br %r1
> >
> > The detour via the execute type instruction has a performance impact.
> > To get rid of the detour the new kernel parameter "nospectre_v2" and
> > "spectre_v2=[on,off,auto]" can be used. If the parameter is specified
> > the kernel and module code will be patched at runtime.
>
> This is really unfortunate naming of kernel option.
>
> spectre_v2=off sounds like we are turning the "bug" off, but i somehow
> suspect you are turning the bug _workaround_ off.
Well, that is the 1:1 copy of the x86 option. Do you want to change that
one as well?
--
blue skies,
Martin.
"Reality continues to ruin my life." - Calvin.
next prev parent reply other threads:[~2018-02-07 11:51 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-07 7:00 [PATCH 0/6] s390: improve speculative execution handling v3 Martin Schwidefsky
2018-02-07 7:00 ` [PATCH 1/6] s390: scrub registers on kernel entry and KVM exit Martin Schwidefsky
2018-02-07 7:00 ` [PATCH 2/6] s390: add optimized array_index_mask_nospec Martin Schwidefsky
2018-02-07 7:00 ` [PATCH 3/6] s390/alternative: use a copy of the facility bit mask Martin Schwidefsky
2018-02-07 7:00 ` [PATCH 4/6] s390: add options to change branch prediction behaviour for the kernel Martin Schwidefsky
2018-02-07 10:02 ` Pavel Machek
2018-02-07 11:49 ` Martin Schwidefsky
2018-02-07 7:00 ` [PATCH 5/6] s390: run user space and KVM guests with modified branch prediction Martin Schwidefsky
2018-02-07 7:00 ` [PATCH 6/6] s390: introduce execute-trampolines for branches Martin Schwidefsky
2018-02-07 10:07 ` Pavel Machek
2018-02-07 11:51 ` Martin Schwidefsky [this message]
2018-02-07 12:07 ` David Woodhouse
2018-02-07 12:17 ` Martin Schwidefsky
2018-02-07 12:20 ` David Woodhouse
2018-02-07 17:55 ` Linus Torvalds
2018-02-07 23:44 ` Masahiro Yamada
2018-02-08 0:05 ` Linus Torvalds
2018-02-08 0:57 ` Kees Cook
2018-02-08 17:11 ` Masahiro Yamada
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