From: Jamie Lokier <jamie@shareable.org>
To: Coywolf Qi Hunt <coywolf@greatcn.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>, linux-kernel@vger.kernel.org
Subject: Re: BOOT_CS
Date: Sat, 21 Feb 2004 16:32:13 +0000 [thread overview]
Message-ID: <20040221163213.GB15991@mail.shareable.org> (raw)
In-Reply-To: <40375261.6030705@greatcn.org>
Coywolf Qi Hunt wrote:
> >(the jump and indirect branch aren't guaranteed to have the
> >proper effects, although technically neither should be required due to
> >the %cr0 write):
>
>
> IMHO, why bother to re-reload %cs again?
>
> In setup.S, %cs is reloaded already. The enable paging code maps the
> address identically, so %cs already contains the proper selector.
It's to flush the instruction prefetch queue: that's one of the side
effects of ljmp.
I recall an Intel manual that said ljmp is required when switching
between real and protected modes, to flush the prefetch queue.
Unfortunately I don't remember what that manual said about just setting PG.
I'd guess that current generation CPUs don't care about ljmp when
changing modes, but older ones certainly do.
-- Jamie
next prev parent reply other threads:[~2004-02-21 16:32 UTC|newest]
Thread overview: 28+ 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 ` Jamie Lokier [this message]
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
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
2004-02-24 10:05 BOOT_CS Etienne Lorrain
2004-02-24 15:39 ` BOOT_CS H. Peter Anvin
2004-02-25 10:30 BOOT_CS Etienne Lorrain
2004-02-25 16:23 ` BOOT_CS H. Peter Anvin
2004-02-26 12:17 BOOT_CS Etienne Lorrain
2004-02-26 21:49 ` BOOT_CS Denis Vlasenko
2004-02-27 10:03 ` BOOT_CS Etienne Lorrain
2004-02-27 18:41 ` BOOT_CS H. Peter Anvin
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