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From: Jon Masters <jcm@jonmasters.org>
To: David Woodhouse <dwmw2@infradead.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	tglx@linutronix.de, x86@kernel.org, kvm@vger.kernel.org,
	torvalds@linux-foundation.org, linux-kernel@vger.kernel.org,
	arjan.van.de.ven@intel.com, dave.hansen@intel.com
Cc: Ingo Molnar <mingo@kernel.org>
Subject: Re: [PATCH 2/2] x86/speculation: Support "Enhanced IBRS" on future CPUs
Date: Mon, 19 Feb 2018 18:37:49 -0500	[thread overview]
Message-ID: <4882860e-23c5-75b3-ac02-c700f615156e@jonmasters.org> (raw)
In-Reply-To: <1518783021.7876.34.camel@infradead.org>

On 02/16/2018 07:10 AM, David Woodhouse wrote:
> On Fri, 2018-02-16 at 12:04 +0100, Paolo Bonzini wrote:
>> On 16/02/2018 11:21, David Woodhouse wrote:

>>> Even if the guest doesn't have/support IBRS_ALL, and is frobbing the
>>> (now emulated) MSR on every kernel entry/exit, that's *still* going to
>>> be a metric shitload faster than what it *thought* it was doing.

Is there any indication/log to the admin that VM doesn't know about
IBRS_ALL and is constantly uselessly writing to an emulated MSR?

While it's probably true that the overhead in time is similar to (or
better than) an actual IBRS MSR write, if the admin/user knows the VM
needs updating, then there's a fighting chance that they might do so.

Jon.

  reply	other threads:[~2018-02-19 23:37 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-02-12 15:27 [PATCH 1/2] x86/speculation: Correct Speculation Control microcode blacklist again David Woodhouse
2018-02-12 15:27 ` [PATCH 2/2] x86/speculation: Support "Enhanced IBRS" on future CPUs David Woodhouse
2018-02-13  7:47   ` Ingo Molnar
2018-02-13  8:12     ` David Woodhouse
2018-02-13  8:02   ` Paolo Bonzini
2018-02-13  8:15     ` David Woodhouse
2018-02-13  9:58       ` Paolo Bonzini
2018-02-13 10:21         ` David Woodhouse
2018-02-13 10:36           ` David Woodhouse
2018-02-13 10:41             ` Paolo Bonzini
2018-02-13 10:53               ` David Woodhouse
2018-02-13 10:55                 ` Paolo Bonzini
2018-02-16  9:58               ` David Woodhouse
2018-02-16 10:08                 ` Paolo Bonzini
2018-02-16 10:21                   ` David Woodhouse
2018-02-16 11:04                     ` Paolo Bonzini
2018-02-16 12:10                       ` David Woodhouse
2018-02-19 23:37                         ` Jon Masters [this message]
2018-02-19 23:42                           ` Van De Ven, Arjan
2018-02-19 23:53                             ` valdis.kletnieks
2018-02-20  0:00                               ` Van De Ven, Arjan
2018-02-20  0:13                                 ` Alan Cox
2018-02-20  0:43                                   ` Linus Torvalds
2018-02-20  1:03                                     ` Alan Cox
2018-02-20  1:08                                       ` Van De Ven, Arjan
2018-02-20  8:52                                     ` Thomas Gleixner
2018-02-20 11:43                                 ` Paolo Bonzini
2018-02-20 14:08                                   ` Van De Ven, Arjan
2018-02-20 14:46                                     ` Paolo Bonzini
2018-02-20 14:59                                       ` Van De Ven, Arjan
2018-02-20 15:09                                         ` Paolo Bonzini
2018-02-23 18:12                                       ` Is: RSB Alternative bit in IA32_ARCH_CAPABILITIES Was:Re: " Konrad Rzeszutek Wilk
2018-02-23 18:18                                         ` Van De Ven, Arjan
2018-02-15 15:21     ` Pavel Machek
2018-02-13  8:57 ` [tip:x86/pti] x86/speculation: Correct Speculation Control microcode blacklist again tip-bot for David Woodhouse

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