linux-kernel - Re: [Xen-devel] Does __KERNEL

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Message-ID: <5707654F.1060407@citrix.com>
Date:	Fri, 8 Apr 2016 09:01:19 +0100
From:	Andrew Cooper <andrew.cooper3@...rix.com>
To:	Andy Lutomirski <luto@...nel.org>, X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:	Borislav Petkov <bp@...en8.de>, kvm list <kvm@...r.kernel.org>,
	xen-devel <Xen-devel@...ts.xen.org>
Subject: Re: [Xen-devel] Does __KERNEL_DS serve a purpose?

On 08/04/2016 01:24, Andy Lutomirski wrote:
> I can't see any reason that we need the __KERNEL_DS segment at all --
> I think that everything that uses __KERNEL_DS could use __USER_DS
> instead.  Am I missing anything?  This has been bugging me for a
> while.
>
> I mulled over this a bit when trying to understand the sysret_ss_attrs
> bug and then forgot about it.

Linux doesn't have a separate __KERNEL_SS.  For the plain data segments,
the dpl is not interesting.

However, %ss is also loaded with __KERNEL_DS, and %ss.dpl is somewhat
important.

~Andrew