Date: Thu, 18 Sep 2003 16:38:31 +0100
From: Jamie Lokier <jamie@shareable.org>
To: Andi Kleen <ak@suse.de>
Cc: Linus Torvalds <torvalds@osdl.org>, Nick Piggin <piggin@cyberone.com.au>,
       Andrew Morton <akpm@osdl.org>, linux-kernel@vger.kernel.org,
       richard.brunner@amd.com
Subject: Re: [PATCH] Athlon/Opteron Prefetch Fix for 2.6.0test5 + numbers
Message-ID: <20030918153831.GA7548@mail.jlokier.co.uk>
References: <20030917202100.GC4723@wotan.suse.de> <Pine.LNX.4.44.0309171332200.2523-100000@laptop.osdl.org> <20030917211200.GA5997@wotan.suse.de>
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Andi Kleen wrote:
> I added a check for LDT entries now. This means prefetch exceptions
> inside non standard code segments will be not handled (I will fix
> that in a follow up patch)

> +	/* Don't check for LDT code segments because they could have
> +	   non zero bases. Better would be to add in the base in this case. */
> +	if (regs->xcs & (1<<2))
> +		return 0;

It is possible to have a non-standard code segment in the GDT, too.
Thus a better to check is "unlikely((regs->xcs & 0xffff) != __USER_CS)".

One way to add in the correct base would be to use the real segment
register.  Don't call __get_user: call your own special function which
uses %gs, and temporarily load regs->xcs into %gs.

Alternatively you can just calculate the base and add it.

-- Jamie
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