From: "Jan Beulich" <JBeulich@suse.com>
To: "Andrew Cooper" <andrew.cooper3@citrix.com>,
"David Vrabel" <david.vrabel@citrix.com>
Cc: <xen-devel@lists.xenproject.org>, <boris.ostrovsky@oracle.com>,
<srostedt@redhat.com>, <linux-kernel@vger.kernel.org>
Subject: Re: [Xen-devel] [PATCH] x86/xen: Fix 32-bit PV guests's usage of kernel_stack
Date: Wed, 09 Apr 2014 16:01:17 +0100 [thread overview]
Message-ID: <53457CDD0200007800007483@nat28.tlf.novell.com> (raw)
In-Reply-To: <53455C21.6000408@citrix.com>
>>> On 09.04.14 at 16:41, <andrew.cooper3@citrix.com> wrote:
> The latter load however can easy fault; The arguments for %ds in
> XSA-42/ CVE-2013-0228 applies to %{e,f,g}s as well.
And it was only that latter operation that I pointed at.
> Furthermore, I am a little concerned about the performance impact of
> this. I would have thought that in most cases, %fs will already be
> correct, at which point reloading it twice is a waste of time.
Why would you expect %fs on the IRET path to commonly point to the
kernel segment rather than whatever user mode wants/needs? Also, I'm
not sure adding conditionals here wouldn't harm performance about as
much as the save/load/restore. If anything I'd look into open coding
GET_THREAD_INFO() without using %fs for this single case.
Jan
next prev parent reply other threads:[~2014-04-09 15:01 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-04-09 14:06 Boris Ostrovsky
2014-04-09 14:08 ` David Vrabel
2014-04-09 14:21 ` [Xen-devel] " Jan Beulich
2014-04-09 14:29 ` David Vrabel
2014-04-09 14:41 ` Andrew Cooper
2014-04-09 15:01 ` Jan Beulich [this message]
2014-04-09 15:38 ` Boris Ostrovsky
2014-04-09 15:40 ` Jan Beulich
2014-04-09 15:25 ` Steven Rostedt
2014-04-09 16:15 ` Boris Ostrovsky
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