linux-kernel - Re: [Fastboot] [PATCH] x86_64: Reload CS when startup

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Message-ID: <aec7e5c30608220153h4553d890v3a3740e7fdc6986@mail.gmail.com>
Date:	Tue, 22 Aug 2006 17:53:26 +0900
From:	"Magnus Damm" <magnus.damm@...il.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	"Andi Kleen" <ak@...e.de>, "Magnus Damm" <magnus@...inux.co.jp>,
	fastboot@...ts.osdl.org, linux-kernel@...r.kernel.org
Subject: Re: [Fastboot] [PATCH] x86_64: Reload CS when startup_64 is used.

Hi Eric,

On 8/22/06, Eric W. Biederman <ebiederm@...ssion.com> wrote:
>
> In long mode the %cs is largely a relic.  However there are a few cases
> like lret where it matters that we have a valid value.  Without this
> patch it is possible to enter the kernel in startup_64 without setting
> %cs to a valid value.  With this patch we don't care what %cs value
> we enter the kernel with, so long as the cs shadow register indicates
> it is a privileged code segment.
>
> Thanks to Magnus Damm for finding this problem and posting the
> first workable patch.  I have moved the jump to set %cs down a
> few instructions so we don't need to take an extra jump.  Which
> keeps the code simpler.
>
> Signed-of-by: Eric W. Biederman <ebiederm@...ssion.com>

While at it, could you please fix up the purgatory code in kexec-tools
to include this fix so we can boot older versions of the kernel too?

Thanks,

/ magnus
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