From: Andrew Cooper <andrew.cooper3@citrix.com>
To: Jan Beulich <jbeulich@suse.com>
Cc: Ian.Jackson@eu.citrix.com, wei.liu2@citrix.com, xen-devel@lists.xen.org
Subject: Re: [PATCH v4 26/26] tools/libxc: Calculate xstate cpuid leaf from guest information
Date: Thu, 7 Apr 2016 12:34:24 +0100 [thread overview]
Message-ID: <570645C0.4020302@citrix.com> (raw)
In-Reply-To: <5705BE4602000078000E5EC5@prv-mh.provo.novell.com>
On 07/04/16 01:56, Jan Beulich wrote:
>>>> Andrew Cooper <andrew.cooper3@citrix.com> 04/07/16 2:40 AM >>>
>> On 07/04/2016 01:16, Jan Beulich wrote:
>>>>>> Andrew Cooper <andrew.cooper3@citrix.com> 04/05/16 7:49 PM >>>
>>>> There is no possible way of avoiding having a whitelist somewhere, which
>>>> limits what Xen will tolerate supporting for the guest.
>>> Right, but preferably in exactly one place. And imo that ought to be
>>> info->xfeature_mask.
>> info->xfeature_mask is actually Xen's limit, as obtained from
>> XEN_DOMCTL_getvcpuextstate, so is an authoritative source of "the
>> maximum Xen will support".
>>
>> However, the guest_xfeature_mask must be generated and used as this
>> patch. Without it, a domU will break if it migrates from a more capable
>> xstate host to a less capable host, as using info->xfeature_mask alone
>> leaks in state which should be levelled out.
>>
>> Currently upstream, heterogeneous migration of domains using xsave is
>> broken if the domain first boots on the more-capable host.
> I don't follow, I'm afraid: To me this looks like two separate things. One is to
> suitably level the guest (via its config file), and the other is to not allow it to
> use things the host doesn't support. If you want the guest to be migratable
> to a less capable host, you need to configure the guest accordingly instead
> of relying on a second instance of white listing.
Agreed, on all points.
But I assert that my change moves the code from being broken to working,
per the above description.
I have reworded several bits for v5 - perhaps that will make the patch
more clear.
~Andrew
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next prev parent reply other threads:[~2016-04-07 11:34 UTC|newest]
Thread overview: 72+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-23 16:36 [PATCH v4 00/26] x86: Improvements to cpuid handling for guests Andrew Cooper
2016-03-23 16:36 ` [PATCH v4 01/26] xen/public: Export cpu featureset information in the public API Andrew Cooper
2016-03-24 14:08 ` Jan Beulich
2016-03-24 14:12 ` Andrew Cooper
2016-03-24 14:16 ` Jan Beulich
2016-03-23 16:36 ` [PATCH v4 02/26] xen/x86: Script to automatically process featureset information Andrew Cooper
2016-03-23 16:36 ` [PATCH v4 03/26] xen/x86: Collect more cpuid feature leaves Andrew Cooper
2016-03-23 16:36 ` [PATCH v4 04/26] xen/x86: Mask out unknown features from Xen's capabilities Andrew Cooper
2016-03-23 16:36 ` [PATCH v4 05/26] xen/x86: Annotate special features Andrew Cooper
2016-03-23 16:36 ` [PATCH v4 06/26] xen/x86: Annotate VM applicability in featureset Andrew Cooper
2016-03-23 16:36 ` [PATCH v4 07/26] xen/x86: Calculate maximum host and guest featuresets Andrew Cooper
2016-03-29 8:57 ` Jan Beulich
2016-03-23 16:36 ` [PATCH v4 08/26] xen/x86: Generate deep dependencies of features Andrew Cooper
2016-03-24 16:16 ` Jan Beulich
2016-03-23 16:36 ` [PATCH v4 09/26] xen/x86: Clear dependent features when clearing a cpu cap Andrew Cooper
2016-03-23 16:36 ` [PATCH v4 10/26] xen/x86: Improve disabling of features which have dependencies Andrew Cooper
2016-03-28 15:18 ` Konrad Rzeszutek Wilk
2016-03-23 16:36 ` [PATCH v4 11/26] xen/x86: Improvements to in-hypervisor cpuid sanity checks Andrew Cooper
2016-03-24 15:38 ` Andrew Cooper
2016-03-24 16:47 ` Jan Beulich
2016-03-24 17:01 ` Andrew Cooper
2016-03-24 17:11 ` Jan Beulich
2016-03-24 17:12 ` Andrew Cooper
2016-03-28 15:29 ` Konrad Rzeszutek Wilk
2016-04-05 15:25 ` Andrew Cooper
2016-03-23 16:36 ` [PATCH v4 12/26] x86/cpu: Move set_cpumask() calls into c_early_init() Andrew Cooper
2016-03-28 15:55 ` Konrad Rzeszutek Wilk
2016-04-05 16:19 ` Andrew Cooper
2016-03-23 16:36 ` [PATCH v4 13/26] x86/cpu: Sysctl and common infrastructure for levelling context switching Andrew Cooper
2016-03-24 16:58 ` Jan Beulich
2016-03-28 16:12 ` Konrad Rzeszutek Wilk
2016-04-05 16:33 ` Andrew Cooper
2016-03-28 17:37 ` Konrad Rzeszutek Wilk
2016-03-23 16:36 ` [PATCH v4 14/26] x86/cpu: Rework AMD masking MSR setup Andrew Cooper
2016-03-28 18:55 ` Konrad Rzeszutek Wilk
2016-04-05 16:44 ` Andrew Cooper
2016-03-23 16:36 ` [PATCH v4 15/26] x86/cpu: Rework Intel masking/faulting setup Andrew Cooper
2016-03-28 19:14 ` Konrad Rzeszutek Wilk
2016-04-05 16:45 ` Andrew Cooper
2016-03-23 16:36 ` [PATCH v4 16/26] x86/cpu: Context switch cpuid masks and faulting state in context_switch() Andrew Cooper
2016-03-28 19:27 ` Konrad Rzeszutek Wilk
2016-04-05 18:34 ` Andrew Cooper
2016-03-23 16:36 ` [PATCH v4 17/26] x86/pv: Provide custom cpumasks for PV domains Andrew Cooper
2016-03-28 19:40 ` Konrad Rzeszutek Wilk
2016-04-05 16:55 ` Andrew Cooper
2016-03-23 16:36 ` [PATCH v4 18/26] x86/domctl: Update PV domain cpumasks when setting cpuid policy Andrew Cooper
2016-03-24 17:04 ` Jan Beulich
2016-03-24 17:05 ` Andrew Cooper
2016-03-28 19:51 ` Konrad Rzeszutek Wilk
2016-03-23 16:36 ` [PATCH v4 19/26] xen+tools: Export maximum host and guest cpu featuresets via SYSCTL Andrew Cooper
2016-03-28 19:59 ` Konrad Rzeszutek Wilk
2016-03-23 16:36 ` [PATCH v4 20/26] tools/libxc: Modify bitmap operations to take void pointers Andrew Cooper
2016-03-28 20:05 ` Konrad Rzeszutek Wilk
2016-03-23 16:36 ` [PATCH v4 21/26] tools/libxc: Use public/featureset.h for cpuid policy generation Andrew Cooper
2016-03-28 20:07 ` Konrad Rzeszutek Wilk
2016-03-23 16:36 ` [PATCH v4 22/26] tools/libxc: Expose the automatically generated cpu featuremask information Andrew Cooper
2016-03-28 20:08 ` Konrad Rzeszutek Wilk
2016-03-23 16:36 ` [PATCH v4 23/26] tools: Utility for dealing with featuresets Andrew Cooper
2016-03-28 20:26 ` Konrad Rzeszutek Wilk
2016-03-23 16:36 ` [PATCH v4 24/26] tools/libxc: Wire a featureset through to cpuid policy logic Andrew Cooper
2016-03-28 20:39 ` Konrad Rzeszutek Wilk
2016-03-23 16:36 ` [PATCH v4 25/26] tools/libxc: Use featuresets rather than guesswork Andrew Cooper
2016-03-23 16:36 ` [PATCH v4 26/26] tools/libxc: Calculate xstate cpuid leaf from guest information Andrew Cooper
2016-03-24 17:20 ` Wei Liu
2016-03-31 7:48 ` Jan Beulich
2016-04-05 17:48 ` Andrew Cooper
2016-04-07 0:16 ` Jan Beulich
2016-04-07 0:40 ` Andrew Cooper
2016-04-07 0:56 ` Jan Beulich
2016-04-07 11:34 ` Andrew Cooper [this message]
2016-03-24 10:27 ` [PATCH v4 00/26] x86: Improvements to cpuid handling for guests Jan Beulich
2016-03-24 10:28 ` Andrew Cooper
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