From: Rene Herman <rene.herman@keyaccess.nl>
To: Jamie Lokier <jamie@shareable.org>
Cc: Coywolf Qi Hunt <coywolf@greatcn.org>,
"H. Peter Anvin" <hpa@zytor.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] Re: BOOT_CS
Date: Mon, 23 Feb 2004 16:24:17 +0100 [thread overview]
Message-ID: <403A1B21.8000100@keyaccess.nl> (raw)
In-Reply-To: <20040223143056.GC30321@mail.shareable.org>
Jamie Lokier wrote:
> Your patch uses two instructions to flush the queue (push+ret) instead
> of one (jmp or ljmp). Is that documented as reliable?
No. The current arch manuals seem to say nothing definite, but Intel's
386 manual (ie, the cpu, not the arch) from 1986 explicitly says "after
setting PG, a jump must follow immediately".
> I can easily imagine an implementation which decodes one instruction
> after a mode change predictably, but not two.
>
> I doubt that it makes a difference - we're setting PG, not changing
> the instruction format - but I'd like us to be sure it cannot fail on
> things like 386s and 486s, and similar non-Intel chips.
I believe you should either keep it as is, do the long jump (although I
don't believe that to be necessary: setup.s already long jumped to us)
or only delete the indirect jump (we've just been longjumped to, and
identity-mapped, so everything would seem to be normalised already).
In any case, please jump directly after setting PG.
Rene.
next prev parent reply other threads:[~2004-02-23 15:24 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-02-21 5:47 BOOT_CS H. Peter Anvin
2004-02-21 12:43 ` BOOT_CS Coywolf Qi Hunt
2004-02-21 16:32 ` BOOT_CS Jamie Lokier
2004-02-23 4:43 ` [PATCH] BOOT_CS Coywolf Qi Hunt
2004-02-23 14:30 ` Jamie Lokier
2004-02-23 15:24 ` Rene Herman [this message]
2004-02-24 3:11 ` [PATCH] Remove the extra jmp Coywolf Qi Hunt
2004-02-24 3:30 ` Brian Gerst
2004-02-24 10:10 ` Coywolf Qi Hunt
2004-02-22 15:13 ` BOOT_CS Eric W. Biederman
2004-02-22 19:47 ` BOOT_CS H. Peter Anvin
2004-02-22 22:05 ` BOOT_CS Eric W. Biederman
2004-02-23 10:27 ` Does Flushing the Queue after PG REALLY a Necessity? Coywolf Qi Hunt
2004-02-23 15:18 ` Philippe Elie
2004-02-24 2:36 ` Coywolf Qi Hunt
2004-02-24 3:10 ` H. Peter Anvin
2004-02-24 4:55 ` Randy.Dunlap
2004-02-24 9:17 ` Coywolf Qi Hunt
2004-02-24 11:21 ` Herbert Poetzl
2004-02-24 11:33 ` Coywolf Qi Hunt
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