From: Paolo Bonzini <pbonzini@redhat.com>
To: "Van De Ven, Arjan" <arjan.van.de.ven@intel.com>,
"valdis.kletnieks@vt.edu" <valdis.kletnieks@vt.edu>
Cc: Jon Masters <jcm@jonmasters.org>,
David Woodhouse <dwmw2@infradead.org>,
"tglx@linutronix.de" <tglx@linutronix.de>,
"x86@kernel.org" <x86@kernel.org>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"torvalds@linux-foundation.org" <torvalds@linux-foundation.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"Hansen, Dave" <dave.hansen@intel.com>,
Ingo Molnar <mingo@kernel.org>
Subject: Re: [PATCH 2/2] x86/speculation: Support "Enhanced IBRS" on future CPUs
Date: Tue, 20 Feb 2018 15:46:57 +0100 [thread overview]
Message-ID: <2159cdc0-c30d-3bf8-1c25-74bff46a1e91@redhat.com> (raw)
In-Reply-To: <0575AF4FD06DD142AD198903C74E1CC87A619465@ORSMSX103.amr.corp.intel.com>
On 20/02/2018 15:08, Van De Ven, Arjan wrote:
>>>> For bonus points: What should happen to a VM that is live migrated
>>>> from one hypervisor to another, and the hypervisors have different
>>>> IBRS support?
>>>
>>> Doctor Doctor it hurts when I do this....
>>>
>>> Migration tends to only work between HV's that are relatively
>>> homogeneous, that's nothing new...
>>
>> No Arjan, this is just wrong. Well, I suppose it's right in the present
>> tense with the IBRS mess on Skylake, but it's _not_ been true until last
>> year.
>
> I meant software wise. You're not going to live migrate from xen to
> kvm or backwards. or between very radically different versions of the
> kvm stack.
Forwards migration to a radically newer version certainly happens. So
when the source hypervisor was too old to tell the VM about IBRS_ALL,
for example, migration should work properly and the VM should perform
well on the destination hypervisor.
Backwards migration to older hypervisors also happens sometimes, but in
general it creates more userspace than kernel issues.
Paolo
next prev parent reply other threads:[~2018-02-20 14:47 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
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 [this message]
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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