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
From: Victor Miasnikov
Date: Wed Apr 17 2013 - 05:10:14 EST
Hi!
Short:
>> When KVM runs in Hyper-V emulation mode it expects to get Hyper-V hypercalls.
>> Mixing KVM hypercalls and Hyper-V requires some tricks. It
VVM>> KVM "Hyper-V emulation" -- this can be related "Linux on Hyper-V" ?
It's not related.
Are You shue?
Xen-team _think_ too what is not related, but has non-100% _full_ emulation of Hyper-V and, as result, create problems
Question is very simple: Hyper-V users/sysadmins need wait patch a-la this:
==
KVM emulates Hyper-V to host enlightened Windows.
. . .
[ hpa: the problem here is that KVM doesn't emulate Hyper-V well
enough, . . ]
. . .
+ * KVM emulates Hyper-V to support enlightened Windows.
+ * Check to see first if we are on a KVM Hypervisor.
+ if (KVM_cpuid_base())
+ return false;
. . .
==
Or "KVM emulates Hyper-V" as "Hyper-V emulates Hyper-V" ?
--
Full:
----- Original Message -----
From: "Michael S. Tsirkin"
To: "K. Y. Srinivasan"
Cc:
Sent: Wednesday, April 17, 2013 10:06 AM
Subject: Re: [PATCH 2/3] X86: Add a check to catch Xen emulation of Hyper-V
On Sun, Feb 03, 2013 at 05:22:38PM -0800, K. Y. Srinivasan wrote:
Xen emulates Hyper-V to host enlightened Windows. Looks like this
emulation may be turned on by default even for Linux guests. Check and
fail Hyper-V detection if we are on Xen.
Signed-off-by: K. Y. Srinivasan kys (at) microsoft.com
I'm very curious what's the specific bug that is fixed here?
I went over the original discussion in
https://patchwork.kernel.org/patch/2064331/
and that's still not clear to me. Is there a configuration
that is broken without this patch but starts working with
this patch?
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.
Could you enlighten me please? :)
Short history of question:
{{
==
> And hypercall has its own set of problems with Windows guests.
> When KVM runs in Hyper-V emulation mode it expects to get Hyper-V hypercalls.
> Mixing KVM hypercalls and Hyper-V requires some tricks. It
Can't we simply register a hypercall ID range with Microsoft?
> may also affect WHQLing Windows drivers since driver will talk to HW
> bypassing Windows interfaces.
Then the WHQL'ed driver doesn't support the PV MMIO hcall?
==
KVM "Hyper-V emulation" -- this can be related "Linux on Hyper-V" ?
}}
{{
>> When KVM runs in Hyper-V emulation mode it expects to get Hyper-V hypercalls.
>> Mixing KVM hypercalls and Hyper-V requires some tricks. It
KVM "Hyper-V emulation" -- this can be related "Linux on Hyper-V" ?
It's not related.
Are You shue?
Xen-team _think_ too what is not related, but has non-100% _full_ emulation of Hyper-V and, as result, create problems:
==
Xen emulates Hyper-V to host enlightened Windows. Looks like this
emulation may be turned on by default even for Linux guests. Check and
fail Hyper-V detection if we are on Xen.
[ hpa: the problem here is that Xen doesn't emulate Hyper-V well
enough, and if the Xen support isn't compiled in, we end up stubling
over the Hyper-V emulation and try to activate it -- and it fails. ]
. . .
+ /*
+ * Xen emulates Hyper-V to support enlightened Windows.
+ * Check to see first if we are on a Xen Hypervisor.
+ */
+ if (xen_cpuid_base())
+ return false;
+
==
}}
Question is very simple: Hyper-V users/sysadmins need wait patch a-la this:
==
KVM emulates Hyper-V to host enlightened Windows. Looks like this
emulation may be turned on by default even for Linux guests. Check and
fail Hyper-V detection if we are on KVM.
[ hpa: the problem here is that KVM doesn't emulate Hyper-V well
enough, and if the KVM support isn't compiled in, we end up stubling
over the Hyper-V emulation and try to activate it -- and it fails. ]
. . .
+ /*
+ * KVM emulates Hyper-V to support enlightened Windows.
+ * Check to see first if we are on a KVM Hypervisor.
+ */
+ if (KVM_cpuid_base())
+ return false;
+
==
Or "KVM emulates Hyper-V" as "Hyper-V emulates Hyper-V" ?
Best regards, Victor Miasnikov
Blog: http://vvm.blog.tut.by/
P.S.
----- Original Message -----
From: "Michael S. Tsirkin"
To: "Victor Miasnikov"
Sent: Wednesday, April 17, 2013 10:07 AM
I'm not sure what are we talking about then, but please
use the mailing list appropriate for the subject.
----- Original Message -----
From: "Victor Miasnikov" vvm (a) tut (dot) by
To: "Michael S. Tsirkin"
Cc: "KY Srinivasan"
Sent: Tuesday, April 16, 2013 9:36 AM
Subject: Are You shue what is 100% _full_ emulation of Hyper-V? Re: It's not related Re: KVM "Hyper-V emulation" -- this
can be related "Linux on Hyper-V" ?
Hi!
>> When KVM runs in Hyper-V emulation mode it expects to get Hyper-V hypercalls.
>> Mixing KVM hypercalls and Hyper-V requires some tricks. It
KVM "Hyper-V emulation" -- this can be related "Linux on Hyper-V" ?
It's not related.
Are You shue?
Xen-team _think_ too what is not related, but has non-100% _full_ emulation of Hyper-V and, as result, create problems:
==
Xen emulates Hyper-V to host enlightened Windows. Looks like this
emulation may be turned on by default even for Linux guests. Check and
fail Hyper-V detection if we are on Xen.
[ hpa: the problem here is that Xen doesn't emulate Hyper-V well
enough, and if the Xen support isn't compiled in, we end up stubling
over the Hyper-V emulation and try to activate it -- and it fails. ]
. . .
+ /*
+ * Xen emulates Hyper-V to support enlightened Windows.
+ * Check to see first if we are on a Xen Hypervisor.
+ */
+ if (xen_cpuid_base())
+ return false;
+
==
( full see ib P.S.)
Best regards, Victor Miasnikov
Blog: http://vvm.blog.tut.by/
P.S.
==
----- Original Message -----
From: "tip-bot for K. Y. Srinivasan"
. . .
Sent: Wednesday, February 13, 2013 3:57 AM
Subject: [tip:x86/hyperv] X86: Add a check to catch Xen emulation of Hyper-V
Commit-ID: db34bbb767bdfa1ebed7214b876fe01c5b7ee457
Gitweb: http://git.kernel.org/tip/db34bbb767bdfa1ebed7214b876fe01c5b7ee457
Author: K. Y. Srinivasan
AuthorDate: Sun, 3 Feb 2013 17:22:38 -0800
Committer: H. Peter Anvin
CommitDate: Tue, 12 Feb 2013 16:27:03 -0800
X86: Add a check to catch Xen emulation of Hyper-V
Xen emulates Hyper-V to host enlightened Windows. Looks like this
emulation may be turned on by default even for Linux guests. Check and
fail Hyper-V detection if we are on Xen.
[ hpa: the problem here is that Xen doesn't emulate Hyper-V well
enough, and if the Xen support isn't compiled in, we end up stubling
over the Hyper-V emulation and try to activate it -- and it fails. ]
Signed-off-by: K. Y. Srinivasan
Link: http://lkml.kernel.org/r/1359940959-32168-2-git-send-email-kys@xxxxxxxxxxxxx
Signed-off-by: H. Peter Anvin
---
arch/x86/kernel/cpu/mshyperv.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index 646d192..4dab317 100644
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -30,6 +30,13 @@ static bool __init ms_hyperv_platform(void)
if (!boot_cpu_has(X86_FEATURE_HYPERVISOR))
return false;
+ /*
+ * Xen emulates Hyper-V to support enlightened Windows.
+ * Check to see first if we are on a Xen Hypervisor.
+ */
+ if (xen_cpuid_base())
+ return false;
+
cpuid(HYPERV_CPUID_VENDOR_AND_MAX_FUNCTIONS,
&eax, &hyp_signature[0], &hyp_signature[1], &hyp_signature[2]);
--
==
----- Original Message -----
From: "Michael S. Tsirkin"
To: "Victor Miasnikov" vvm (a) tut (dot) by
Sent: Tuesday, April 16, 2013 1:11 AM
Subject: Re: KVM "Hyper-V emulation" -- this can be related "Linux on Hyper-V" ? Fw: When KVM runs in Hyper-V emulation
mode it expects to get Hyper-V hypercalls.
On Mon, Apr 15, 2013 at 04:00:34PM +0300, Victor Miasnikov wrote:
==
>> And hypercall has its own set of problems with Windows guests.
>> When KVM runs in Hyper-V emulation mode it expects to get Hyper-V hypercalls.
>> Mixing KVM hypercalls and Hyper-V requires some tricks. It
>
>Can't we simply register a hypercall ID range with Microsoft?
>
>> may also affect WHQLing Windows drivers since driver will talk to HW
>> bypassing Windows interfaces.
>
>Then the WHQL'ed driver doesn't support the PV MMIO hcall?
==
KVM "Hyper-V emulation" -- this can be related "Linux on Hyper-V" ?
It's not related.
----- Original Message -----
From: "Victor Miasnikov" vvm (a) tut (dot) by
To: "Michael S. Tsirkin"
Sent: Monday, April 15, 2013 4:00 PM
Subject: KVM "Hyper-V emulation" -- this can be related "Linux on Hyper-V" ? Fw: When KVM runs in Hyper-V emulation mode
it expects to get Hyper-V hypercalls.
Hi!
==
> And hypercall has its own set of problems with Windows guests.
> When KVM runs in Hyper-V emulation mode it expects to get Hyper-V hypercalls.
> Mixing KVM hypercalls and Hyper-V requires some tricks. It
Can't we simply register a hypercall ID range with Microsoft?
> may also affect WHQLing Windows drivers since driver will talk to HW
> bypassing Windows interfaces.
Then the WHQL'ed driver doesn't support the PV MMIO hcall?
==
KVM "Hyper-V emulation" -- this can be related "Linux on Hyper-V" ?
Best regards, Victor Miasnikov
Blog: http://vvm.blog.tut.by/
--
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