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From: Andrew Cooper <andrew.cooper3@citrix.com>
To: speck@linutronix.de
Subject: [MODERATED] Re: [patch V10 00/10] Control knobs and Documentation 0
Date: Fri, 13 Jul 2018 17:56:07 +0100	[thread overview]
Message-ID: <267cd39e-263e-e291-b72f-630ae121eaf4@citrix.com> (raw)
In-Reply-To: <6e2b04bb-4786-ae48-1fe8-e1bbdbcd8b92@redhat.com>

On 13/07/18 17:22, speck for Paolo Bonzini wrote:
> On 12/07/2018 16:19, speck for Thomas Gleixner wrote:
>> The following series provides the following changes:
>>
>>   - Fix EPT=off handling so it avoids flushing
>>   
>>   - Expose proper VMX mitigation information in sysfs
>>
>>   - Drops the MSR list mechanism for flush 'always' to prepare for runtime
>>     control. The default flush mechanism is conditional anyway and the MSR
>>     list is set up at guest init time, which is nasty to run time switch
>>     especially because the static key is a global control which can be
>>     flipped by an update.
>>
>>   - Make the flush always/conditional static key based.
>>
>>   - Serialize the kvm parameter setter function
>>
>>   - Enable runtime control for the kvm parameter
>>
>>   - Add the l1tf command line option. It's not run time controllable as it
>>     does not make sense to have 3 knobs at runtime. For the command line
>>     the combo knob setting the default is convenient
>>
>>   - Documentation update
>>
>> This takes the review comments into account as much as still applicable.
>>
>> Thanks to Jiri for testing the lot and debugging and fixing my brainfarts!
>>
>> Git bundle follows in separate mail.
> Another case on top of this series...
>
> ---------------------- 8< --------------------
> From a0f605fed99cf1623f8716b22c11113653c258a3 Mon Sep 17 00:00:00 2001
> From: Paolo Bonzini <pbonzini@redhat.com>
> Date: Fri, 13 Jul 2018 18:15:29 +0200
> Subject: [PATCH] kvm: vmx: disable L1D flush when running as a nested
>  hypervisor
>
> VMENTER operations from the nested hypervisor into the nested guest
> will always be processed by the bare metal hypervisor.  Therefore,
> when running as a nested hypervisor, doing L1D cache flushes on vmentry
> will result in twice the work and twice the slowdown, for no benefit.

Only if your outer hypervisor says so by setting MSR_ARCH_CAPS.VMENTRY_NO

In all other circumstances, it is not safe to make this assumption.

~Andrew

  reply	other threads:[~2018-07-13 16:56 UTC|newest]

Thread overview: 49+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-07-12 14:19 [patch V10 00/10] Control knobs and Documentation 0 Thomas Gleixner
2018-07-12 14:19 ` [patch V10 01/10] Control knobs and Documentation 1 Thomas Gleixner
2018-07-12 15:34   ` [MODERATED] " Greg KH
2018-07-12 15:38     ` Thomas Gleixner
2018-07-12 15:46       ` Thomas Gleixner
2018-07-12 17:08         ` [MODERATED] " Greg KH
2018-07-12 14:19 ` [patch V10 02/10] Control knobs and Documentation 2 Thomas Gleixner
2018-07-12 17:09   ` [MODERATED] " Greg KH
2018-07-12 14:19 ` [patch V10 03/10] Control knobs and Documentation 3 Thomas Gleixner
2018-07-12 16:13   ` [MODERATED] " Josh Poimboeuf
2018-07-13  9:10     ` Thomas Gleixner
2018-07-12 17:09   ` [MODERATED] " Greg KH
2018-07-12 14:19 ` [patch V10 04/10] Control knobs and Documentation 4 Thomas Gleixner
2018-07-12 17:10   ` [MODERATED] " Greg KH
2018-07-12 14:19 ` [patch V10 05/10] Control knobs and Documentation 5 Thomas Gleixner
2018-07-12 17:10   ` [MODERATED] " Greg KH
2018-07-12 14:19 ` [patch V10 06/10] Control knobs and Documentation 6 Thomas Gleixner
2018-07-12 16:14   ` [MODERATED] " Josh Poimboeuf
2018-07-12 17:10   ` Greg KH
2018-07-12 14:19 ` [patch V10 07/10] Control knobs and Documentation 7 Thomas Gleixner
2018-07-12 17:11   ` [MODERATED] " Greg KH
2018-07-12 14:19 ` [patch V10 08/10] Control knobs and Documentation 8 Thomas Gleixner
2018-07-12 16:22   ` [MODERATED] " Josh Poimboeuf
2018-07-12 17:12     ` Greg KH
2018-07-13  9:18     ` Thomas Gleixner
2018-07-12 17:17   ` [MODERATED] " Greg KH
2018-07-12 14:19 ` [patch V10 09/10] Control knobs and Documentation 9 Thomas Gleixner
2018-07-12 16:24   ` [MODERATED] " Josh Poimboeuf
2018-07-12 17:17     ` Greg KH
2018-07-12 17:16   ` Greg KH
2018-07-15  3:12   ` Kees Cook
2018-07-12 14:19 ` [patch V10 10/10] Control knobs and Documentation 10 Thomas Gleixner
2018-07-12 16:03   ` [MODERATED] " Linus Torvalds
2018-07-12 16:31     ` Peter Zijlstra
2018-07-12 16:13   ` Josh Poimboeuf
2018-07-12 16:26     ` Josh Poimboeuf
2018-07-13  9:09     ` Thomas Gleixner
2018-07-12 17:18   ` [MODERATED] " Greg KH
2018-07-15  7:30   ` Borislav Petkov
2018-07-27 16:41   ` Dave Hansen
2018-07-12 14:54 ` [patch V10 00/10] Control knobs and Documentation 0 Thomas Gleixner
2018-07-12 19:30 ` [MODERATED] " Josh Poimboeuf
2018-07-13 15:03   ` Thomas Gleixner
2018-07-13  8:30 ` [MODERATED] " Jiri Kosina
2018-07-13 16:22 ` Paolo Bonzini
2018-07-13 16:56   ` Andrew Cooper [this message]
2018-07-13 17:01     ` Paolo Bonzini
2018-07-13 17:28   ` Konrad Rzeszutek Wilk
2018-07-15 13:58     ` Paolo Bonzini

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