KVM "Hyper-V emulation" -- this can be related "Linux on Hyper-V" ? Or "KVM emulates Hyper-V" as "Hyper-V emulates Hyper-V" ? Re: [PATCH 2/3] X86: Add a check to catch Xen emulation of Hyper-V
vvm at tut.by
Wed Apr 17 13:49:16 UTC 2013
2013/4/17 Jan Beulich
> >>> On 17.04.13 at 12:16, "Michael S. Tsirkin" wrote:
> > If the hypervisor says it's Hyper-V, that's because it wants
> > guests to use Hyper-V. I don't see why is guest second-guessing
> > this a good idea.
> There are two reasons here: For one, when the hypervisor is not
> Hyper-V, but is providing some Hyper-V emulation, that's intended
> for Windows guests to use, not e.g. Linux ones, especially when
> such guests could use the native hypervisor interface with much
> greater benefit.
> And second, there reportedly are features of (newer?) Hyper-V
> that some emulation may not provide, but that are also not easily
> On Wed, Apr 17, 2013 at 12:10:01PM +0300, Victor Miasnikov wrote:
>> Question is very simple: Hyper-V users/sysadmins need wait patch a-la this:
>> Or "KVM_and_or_XEN_or_other_Hypervisor_what_has_non-full-emulation_of_Hyper-V emulates Hyper-V" as "Hyper-V emulates
>> Hyper-V" ?
> No. You are using Hyper-V, not the KVM_and_or_XEN_or_other_Hypervisor_what_has_non-full-emulation_of_Hyper-V
> emulation of it.
> No patches dealing with this emulation should have any effect on you.
This is _positive_ variant of possible future,
but on _practic_ very often we need prevent _negative_ variant of possible future
>> + /*
>> + * KVM_and_or_XEN_or_other_Hypervisor_what_has_non-full-emulation_of_Hyper-V emulates Hyper-V to support
>> enlightened Windows.
>> + * Check to see first if we are on a KVM_and_or_XEN_or_other_Hypervisor_what_has_non-full-emulation_of_Hyper-V
>> + */
>> + if (KVM_and_or_XEN_or_other_Hypervisor_what_has_non-full-emulation_of_Hyper-V_cpuid_base())
>> + return false;
> If the hypervisor says it's Hyper-V, that's because it wants guests to use Hyper-V.
Even if guest ( i.e. Virtual Computer) contain Linux OS ?
>> KVM_and_or_XEN_or_other_Hypervisor_what_has_non-full-emulation_of_Hyper-V emulates Hyper-V to host enlightened
>> . . .
>> [ hpa: the problem here is that
>> KVM_and_or_XEN_or_other_Hypervisor_what_has_non-full-emulation_of_Hyper-V doesn't emulate Hyper-V well enough, .
>> . ]
> What's emulated not well enough?
In case of XEN variant non-full-emulation_of_Hyper-V , IMHO :
----- Original Message -----
From: "Victor Miasnikov"
To: "Michael S. Tsirkin"
Sent: Wednesday, April 17, 2013 12:41 PM
Subject: IMHO, XEN emulation of Hyper-V not contain needed clocksource for Lunux guest Re: [PATCH 2/3] X86: Add a check
to catch Xen emulation of Hyper-V
> It seems that one might want to use hyper-v emulation e.g. to test
> hyper-v code without using windows, so the functionality
> that this patch disables is not completely useless,
> so there should be a good reason for disabling it.
As I undestand, XEN emulation of Hyper-V not contain needed clocksource for Lunux guest ( virtual computers)
I.e. Linux VM "think" what is running on Hyper-V host call clocksource_register_hz(&hyperv_cs, NSEC_PER_SEC/100)
and a-la BSOD or vice versa . . .
> I went over the original discussion in
> and that's still not clear to me. Is there a configuration
> that is broken without this patch but starts working with
> this patch?
IMHO, this related to:
- clocksource_register_hz(&hyperv_cs, NSEC_PER_SEC/100);
+ if (ms_hyperv.features & HV_X64_MSR_TIME_REF_COUNT_AVAILABLE)
+ clocksource_register_hz(&hyperv_cs, NSEC_PER_SEC/100);
Date Tue, 12 Feb 2013 16:56:07 -0800
From tip-bot for Olaf Hering
Subject [tip:x86/hyperv] x86: Hyper-V: register clocksource only if its advertised
. . .
Best regards, Victor Miasnikov
Best regards, Victor Miasnikov
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