From: "H. Peter Anvin" <hpa@zytor.com>
To: Stefan Bader <stefan.bader@canonical.com>
Cc: wei.y.yang@intel.com,
"xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>,
haitao.shan@intel.com, xin.li@intel.com,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Subject: Re: Xen HVM regression on certain Intel CPUs
Date: Wed, 27 Mar 2013 10:23:59 -0700 [thread overview]
Message-ID: <51532B2F.60506@zytor.com> (raw)
In-Reply-To: <5153299A.7070108@canonical.com>
On 03/27/2013 10:17 AM, Stefan Bader wrote:
>> What does x86info and /proc/cpuinfo show in HVM?
>
> x86info cpuid[7].ebx = 0xbbb and /proc/cpuinfo also shows smep
> set.
On all CPUs?
>> The inbound %cr4 shouldn't matter at all, we try to not rely on
>> it.
>>
>> If the hypervisor presents SMEP to the guest then the guest is
>> pretty obviously going to try to use it.
>
> To me it looks like when bootstrapping the APs things are not yet
> ready to use it. If I did not miss something, the only place that
> the saved contents of cr4 are used is in startup_32 when the cpus
> are brought up. And then just stop dead. Would need to read more
> code but a bit weird why the BP is not affected.
This feels like a bug in Xen, but I don't know for sure yet. Either
which way, it is odd. That write to cr4 should be entirely legitimate.
-hpa
next prev parent reply other threads:[~2013-03-27 17:23 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 [this message]
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
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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