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From: "Jan Beulich" <JBeulich@suse.com>
To: "K. Y. Srinivasan" <kys@microsoft.com>
Cc: <olaf@aepfle.de>, <bp@alien8.de>, <apw@canonical.com>,
	<x86@kernel.org>, <tglx@linutronix.de>,
	<devel@linuxdriverproject.org>, <gregkh@linuxfoundation.org>,
	<jasowang@redhat.com>, <linux-kernel@vger.kernel.org>,
	<hpa@zytor.com>
Subject: Re: [PATCH 2/3] X86: Add a check to catch Xen emulation of Hyper-V
Date: Wed, 30 Jan 2013 08:53:27 +0000	[thread overview]
Message-ID: <5108ED9702000078000BAA08@nat28.tlf.novell.com> (raw)
In-Reply-To: <1359507108-26091-2-git-send-email-kys@microsoft.com>

>>> On 30.01.13 at 01:51, "K. Y. Srinivasan" <kys@microsoft.com> 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@microsoft.com>
> ---
>  arch/x86/kernel/cpu/mshyperv.c |    7 +++++++
>  1 files changed, 7 insertions(+), 0 deletions(-)
> 
> 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]);

I'm not convinced that's the right approach - any hypervisor
could do similar emulation, and hence you either want to make
sure you run on Hyper-V (by excluding all others), or you
tolerate using the emulation (which may require syncing up with
the other guest implementations so that shared resources don't
get used by two parties).

I also wonder whether using the Hyper-V emulation (where
useful, there might not be anything right now, but this may
change going forward) when no Xen support is configured
wouldn't be better than not using anything...

Jan


  reply	other threads:[~2013-01-30  8:53 UTC|newest]

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-01-30  0:51 [PATCH 0/3] X86: Deliver Hyper-V interrupts on a seperate IDT vector K. Y. Srinivasan
2013-01-30  0:51 ` [PATCH 1/3] x86: Hyper-V: register clocksource only if its advertised K. Y. Srinivasan
2013-01-30  0:51   ` [PATCH 2/3] X86: Add a check to catch Xen emulation of Hyper-V K. Y. Srinivasan
2013-01-30  8:53     ` Jan Beulich [this message]
2013-01-30 18:12       ` KY Srinivasan
2013-01-30 18:19         ` H. Peter Anvin
2013-01-31  7:37         ` Jan Beulich
2013-01-31 14:46           ` KY Srinivasan
2013-01-31 15:53             ` KY Srinivasan
2013-01-31 16:45               ` Jan Beulich
2013-01-31 18:29                 ` H. Peter Anvin
2013-01-31 21:41       ` H. Peter Anvin
2013-02-01 13:19         ` Stefano Stabellini
2013-02-01 15:10           ` KY Srinivasan
2013-02-01 19:34             ` KY Srinivasan
2013-01-30  0:51   ` [PATCH 3/3] X86: Handle Hyper-V vmbus interrupts as special hypervisor interrupts K. Y. Srinivasan
2013-01-30  8:58     ` Jan Beulich
2013-01-31 14:55       ` KY Srinivasan
2013-02-04  1:21 [PATCH 0/3] X86: Deliver Hyper-V interrupts on a seperate IDT vector K. Y. Srinivasan
2013-02-04  1:22 ` [PATCH 1/3] x86: Hyper-V: register clocksource only if its advertised K. Y. Srinivasan
2013-02-04  1:22   ` [PATCH 2/3] X86: Add a check to catch Xen emulation of Hyper-V K. Y. Srinivasan
2013-04-17  7:06     ` Michael S. Tsirkin
2013-04-17 13:20       ` KY Srinivasan
2013-04-17 12:48         ` Michael S. Tsirkin
2013-04-17 14:12           ` KY Srinivasan
2013-04-17 13:25             ` Michael S. Tsirkin
2013-04-17 14:34               ` KY Srinivasan
2013-04-17 13:48                 ` Michael S. Tsirkin
2013-04-17 15:31                   ` KY Srinivasan
2013-04-17 15:50                     ` Jan Beulich
2013-04-17 16:28                       ` KY Srinivasan
2013-04-18  7:48                         ` Michael S. Tsirkin
2013-04-18 13:23                           ` KY Srinivasan
2013-04-18 13:30                             ` KY Srinivasan
2013-04-17 13:52         ` Jan Beulich
2013-04-17 13:01           ` Michael S. Tsirkin
2013-04-17 13:11             ` Michael S. Tsirkin
2013-04-17 14:09             ` Jan Beulich
2013-04-17 15:17               ` H. Peter Anvin

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