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From: "Wu, Feng" <feng.wu@intel.com>
To: Jan Beulich <JBeulich@suse.com>,
	xen-devel <xen-devel@lists.xenproject.org>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>,
	Keir Fraser <keir@xen.org>, "Wu, Feng" <feng.wu@intel.com>
Subject: Re: [PATCH v3 0/4] x86: accommodate 32-bit PV guests with SMEP/SMAP handling
Date: Tue, 21 Jun 2016 06:19:06 +0000	[thread overview]
Message-ID: <E959C4978C3B6342920538CF579893F019725043@SHSMSX103.ccr.corp.intel.com> (raw)
In-Reply-To: <56EA6FDF02000078000DD8FB@prv-mh.provo.novell.com>



> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@suse.com]
> Sent: Thursday, March 17, 2016 3:51 PM
> To: xen-devel <xen-devel@lists.xenproject.org>
> Cc: Andrew Cooper <andrew.cooper3@citrix.com>; Wu, Feng
> <feng.wu@intel.com>; Keir Fraser <keir@xen.org>
> Subject: [PATCH v3 0/4] x86: accommodate 32-bit PV guests with SMEP/SMAP
> handling
> 
> 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?

Thanks,
Feng

> 
> 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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  parent reply	other threads:[~2016-06-21  6:19 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 [this message]
2016-06-21  7:17         ` Jan Beulich

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