From: Stefan Bader <stefan.bader@canonical.com>
To: Keir Fraser <keir.xen@gmail.com>
Cc: "xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
wei.y.yang@intel.com, haitao.shan@intel.com, xin.li@intel.com,
"H. Peter Anvin" <hpa@zytor.com>
Subject: Re: Xen HVM regression on certain Intel CPUs
Date: Thu, 28 Mar 2013 16:06:37 +0100 [thread overview]
Message-ID: <51545C7D.2040608@canonical.com> (raw)
In-Reply-To: <CD79061A.1F6E4%keir.xen@gmail.com>
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On 27.03.2013 21:24, Keir Fraser wrote:
> On 27/03/2013 16:45, "Stefan Bader" <stefan.bader@canonical.com> wrote:
>
>>>> Seems that I was relying on the wrong source of information when checking
>>>> SMEP
>>>> support. The cpuid command seems at fail. But /proc/cpuinfo reports it. So
>>>> that
>>>> at least explains where that comes from... sorry for that.
>>>
>>> OK, so if you boot Xen with smep=1 (which disables SMEP, kind of
>>> counterintuive flag)
>>> that would work fine?
>>
>> Rebooting with smep=1 as a hv argument does not fix it. But I would be careful
>> since I just quickly did this without checking whether Xen 4.2.1 undestands
>> the
>> flag already.
>
> Yes, the flag is understood by all Xen 4.2 releases. However it is not
> inverted as you believe: it really is smep=0 or smep=off or even no-smep to
> disable SMEP. smep=1 will enable SMEP (which is the default anyway).
>
> I also checked how CPUID.SMEP gets set for an HVM guest, and it is very
> obviously masked off if SMEP support has been disabled or is unavailable. So
> I do not think we can be erroneously passing the CPUID flag to the guest.
No you are completely right. The inverse boolean got me for good. So to summarize:
- smep=0 as hypervisor argument avoids the problem for all guests
- nosmep as hvm guest arguement avoids the problem for that guest
- /proc/cpuinfo correctly reflects whether smep has been masked off or not
>
> -- Keir
>
>
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xen.org
> http://lists.xen.org/xen-devel
>
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next prev parent reply other threads:[~2013-03-28 15:06 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-03-27 15:26 Xen HVM regression on certain Intel CPUs Stefan Bader
2013-03-27 15:53 ` Stefan Bader
2013-03-27 16:04 ` Konrad Rzeszutek Wilk
2013-03-27 16:09 ` H. Peter Anvin
2013-03-27 16:24 ` Stefan Bader
2013-03-27 16:32 ` H. Peter Anvin
2013-03-27 16:32 ` Stefano Stabellini
2013-03-27 16:45 ` Stefan Bader
2013-03-27 16:52 ` H. Peter Anvin
2013-03-27 17:17 ` Stefan Bader
2013-03-27 17:23 ` H. Peter Anvin
2013-03-27 17:38 ` Stefan Bader
2013-03-28 13:34 ` Jan Beulich
2013-03-28 15:02 ` Stefan Bader
2013-03-28 16:39 ` Stefan Bader
2013-04-03 11:56 ` Stefan Bader
2013-04-03 12:43 ` Jan Beulich
2013-04-03 14:28 ` Keir Fraser
2013-04-03 15:00 ` Xu, Dongxiao
2013-04-03 15:48 ` H. Peter Anvin
2013-04-03 16:05 ` Jan Beulich
2013-03-27 17:28 ` Stefan Bader
2013-03-27 17:30 ` H. Peter Anvin
2013-03-27 17:40 ` Stefan Bader
2013-03-27 17:44 ` H. Peter Anvin
2013-03-27 20:24 ` Keir Fraser
2013-03-28 15:06 ` Stefan Bader [this message]
2013-03-28 15:42 ` H. Peter Anvin
2013-03-28 16:12 ` Stefan Bader
2013-03-27 16:18 ` H. Peter Anvin
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