From: "Jan Beulich" <JBeulich@suse.com>
To: Feng Wu <feng.wu@intel.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>,
Keir Fraser <keir@xen.org>,
xen-devel <xen-devel@lists.xenproject.org>
Subject: Re: [PATCH v3 0/4] x86: accommodate 32-bit PV guests with SMEP/SMAP handling
Date: Tue, 21 Jun 2016 01:17:48 -0600 [thread overview]
Message-ID: <5769063C02000078000F716D@prv-mh.provo.novell.com> (raw)
In-Reply-To: <E959C4978C3B6342920538CF579893F019725043@SHSMSX103.ccr.corp.intel.com>
>>> On 21.06.16 at 08:19, <feng.wu@intel.com> wrote:
>> From: Jan Beulich [mailto:JBeulich@suse.com]
>> Sent: Thursday, March 17, 2016 3:51 PM
>>
>> As has been explained previously[1], SMAP (and with less relevance
>> also SMEP) is not compatible with 32-bit PV guests which aren't
>> aware/prepared to be run with that feature enabled. Andrew's
>> original approach either sacrificed architectural correctness for
>> making 32-bit guests work again, or disabled SMAP also for not
>> insignificant portions of hypervisor code, both by allowing to control
>> the workaround mode via command line option.
>
> Hi Jan, do you mind sharing more about Andrew's original approach?
> And to solve this issue can we just disable SMEP/SMAP for Xen itself,
> hence only HVM will benefit from this feature?
Did you look at the link still visible below? If you did, please be more
precise about the details you need.
>> This alternative approach disables SMEP and SMAP only while
>> running 32-bit PV guest code plus a few hypervisor instructions
>> early after entering hypervisor context from or late before exiting
>> to such guests. Those few instructions (in assembly source) are of
>> course much easier to prove not to perform undue memory
>> accesses than code paths reaching deep into C sources.
>>
>> The 4th patch really is unrelated except for not applying cleanly
>> without the earlier ones, and the potential having been noticed
>> while putting together the 2nd one.
>>
>> 1: move cached CR4 value to struct cpu_info
>> 2: suppress SMEP and SMAP while running 32-bit PV guest code
>> 3: use optimal NOPs to fill the SMEP/SMAP placeholders
>> 4: use 32-bit loads for 32-bit PV guest state reload
>>
>> Signed-off-by: Jan Beulich <jbeulich@suse.com>
>> ---
>> v3: New patch 1, as a prereq to changes in patch 2 (previously
>> 1). The primary reason for this are performance issues that
>> have been found by Andrew with the previous version.
>> v2: Various changes to patches 1 and 2 - see there.
>>
>> [1] http://lists.xenproject.org/archives/html/xen-devel/2015-06/msg03888.html
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prev parent reply other threads:[~2016-06-21 7:17 UTC|newest]
Thread overview: 67+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-04 11:08 [PATCH 0/4] x86: accommodate 32-bit PV guests with SMAP/SMEP handling Jan Beulich
2016-03-04 11:27 ` [PATCH 1/4] x86/alternatives: correct near branch check Jan Beulich
2016-03-07 15:43 ` Andrew Cooper
2016-03-07 15:56 ` Jan Beulich
2016-03-07 16:11 ` Andrew Cooper
2016-03-07 16:21 ` Jan Beulich
2016-03-08 17:33 ` Andrew Cooper
2016-03-04 11:27 ` [PATCH 2/4] x86: suppress SMAP and SMEP while running 32-bit PV guest code Jan Beulich
2016-03-07 16:59 ` Andrew Cooper
2016-03-08 7:57 ` Jan Beulich
2016-03-09 8:09 ` Wu, Feng
2016-03-09 14:09 ` Jan Beulich
2016-03-09 11:19 ` Andrew Cooper
2016-03-09 14:28 ` Jan Beulich
2016-03-09 8:09 ` Wu, Feng
2016-03-09 10:45 ` Andrew Cooper
2016-03-09 12:27 ` Wu, Feng
2016-03-09 12:33 ` Andrew Cooper
2016-03-09 12:36 ` Jan Beulich
2016-03-09 12:54 ` Wu, Feng
2016-03-09 13:35 ` Wu, Feng
2016-03-09 13:42 ` Andrew Cooper
2016-03-09 14:03 ` Jan Beulich
2016-03-09 14:07 ` Jan Beulich
2016-03-04 11:28 ` [PATCH 3/4] x86: use optimal NOPs to fill the SMAP/SMEP placeholders Jan Beulich
2016-03-07 17:43 ` Andrew Cooper
2016-03-08 8:02 ` Jan Beulich
2016-03-04 11:29 ` [PATCH 4/4] x86: use 32-bit loads for 32-bit PV guest state reload Jan Beulich
2016-03-07 17:45 ` Andrew Cooper
2016-03-10 9:44 ` [PATCH v2 0/3] x86: accommodate 32-bit PV guests with SMEP/SMAP handling Jan Beulich
2016-03-10 9:53 ` [PATCH v2 1/3] x86: suppress SMEP and SMAP while running 32-bit PV guest code Jan Beulich
2016-05-13 15:48 ` Andrew Cooper
2016-03-10 9:54 ` [PATCH v2 2/3] x86: use optimal NOPs to fill the SMEP/SMAP placeholders Jan Beulich
2016-05-13 15:49 ` Andrew Cooper
2016-03-10 9:55 ` [PATCH v2 3/3] x86: use 32-bit loads for 32-bit PV guest state reload Jan Beulich
[not found] ` <56E9A0DB02000078000DD54C@prv-mh.provo.novell.com>
2016-03-17 7:50 ` [PATCH v3 0/4] x86: accommodate 32-bit PV guests with SMEP/SMAP handling Jan Beulich
2016-03-17 8:02 ` [PATCH v3 1/4] x86: move cached CR4 value to struct cpu_info Jan Beulich
2016-03-17 16:20 ` Andrew Cooper
2016-03-17 8:03 ` [PATCH v3 2/4] x86: suppress SMEP and SMAP while running 32-bit PV guest code Jan Beulich
2016-03-25 18:01 ` Konrad Rzeszutek Wilk
2016-03-29 6:55 ` Jan Beulich
2016-05-13 15:58 ` Andrew Cooper
2016-03-17 8:03 ` [PATCH v3 3/4] x86: use optimal NOPs to fill the SMEP/SMAP placeholders Jan Beulich
2016-05-13 15:57 ` Andrew Cooper
2016-05-13 16:06 ` Jan Beulich
2016-05-13 16:09 ` Andrew Cooper
2016-03-17 8:04 ` [PATCH v3 4/4] x86: use 32-bit loads for 32-bit PV guest state reload Jan Beulich
2016-03-25 18:02 ` Konrad Rzeszutek Wilk
2016-03-17 16:14 ` [PATCH v3 5/4] x86: reduce code size of struct cpu_info member accesses Jan Beulich
2016-03-25 18:47 ` Konrad Rzeszutek Wilk
2016-03-29 6:59 ` Jan Beulich
2016-03-30 14:28 ` Konrad Rzeszutek Wilk
2016-03-30 14:42 ` Jan Beulich
2016-05-13 16:11 ` Andrew Cooper
2016-05-03 13:58 ` Ping: [PATCH v3 2/4] x86: suppress SMEP and SMAP while running 32-bit PV guest code Jan Beulich
2016-05-03 14:10 ` Andrew Cooper
2016-05-03 14:25 ` Jan Beulich
2016-05-04 10:03 ` Andrew Cooper
2016-05-04 13:35 ` Jan Beulich
2016-05-04 3:07 ` Wu, Feng
2016-05-13 15:21 ` Wei Liu
2016-05-13 15:30 ` Jan Beulich
2016-05-13 15:33 ` Wei Liu
2016-05-13 17:02 ` [PATCH v3 0/4] x86: accommodate 32-bit PV guests with SMEP/SMAP handling Wei Liu
2016-05-13 17:21 ` Andrew Cooper
2016-06-21 6:19 ` Wu, Feng
2016-06-21 7:17 ` Jan Beulich [this message]
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