linux-kernel - Re: [PATCH RESEND 1/1] X86: Handle Hyper-V vmbus interrupts as special hypervisor interrupts

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Message-ID: <20130125135834.GA18361@aepfle.de>
Date:	Fri, 25 Jan 2013 14:58:35 +0100
From:	Olaf Hering <olaf@...fle.de>
To:	Jan Beulich <JBeulich@...e.com>
Cc:	KY Srinivasan <kys@...rosoft.com>, "bp@...en8.de" <bp@...en8.de>,
	"apw@...onical.com" <apw@...onical.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"jasowang@...hat.com" <jasowang@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"hpa@...or.com" <hpa@...or.com>
Subject: Re: [PATCH RESEND 1/1] X86: Handle Hyper-V vmbus interrupts as
 special hypervisor interrupts

On Fri, Jan 25, Jan Beulich wrote:

> >>> On 24.01.13 at 19:59, Olaf Hering <olaf@...fle.de> wrote:
> > On Thu, Jan 24, KY Srinivasan wrote:
> > 
> > 
> >> > Question is - considering you stated that this is supported
> >> > starting in Win8, doesn't Hyper-V itself announce that
> >> > capability in some explicit way?
> >> 
> >> Thanks Jan. Unfortunately I don't think tis interrupt delivery model
> >> is specified via a "feature" bit (I will check with the Windows guys).
> >> Perhaps, we can have a Hyper-V specific compilation switch to address
> >> the Xen emulation issue.
> > 
> > Would that really help if both pvops XEN_PVHVM and HYPERV are enabled in
> > the config? I assume at this point the access to the DMI data is not yet
> > possible.
> 
> As just said in another reply - with XEN_PVHVM, there's no problem,
> since Xen gets checked for first. There's only a problem when
> !XEN_PVHVM, because in that case Hyper-V will be probed for.
> And the problem can only get bigger when on top of that the
> out-of-tree PV drivers are intended to be used.

Yes, xen_cpuid_base() recognizes Xen as hypervisor even with
'viridian=1' in the .cfg file.
 I think if there is no feature bit for this, the DMI can be used
because its appearently available before the host is checked:

...
[    0.000000] NX (Execute Disable) protection: active
[    0.000000] DMI 2.4 present.
[    0.000000] DMI: Xen HVM domU, BIOS 4.1.3_06-0.7.1 12/05/2012
[    0.000000] Hypervisor detected: Microsoft HyperV
[    0.000000] HyperV: features 0x70, hints 0x0
[    0.000000] e820 update range: 0000000000000000 - 0000000000010000 (usable) ==> (reserved)
...

Olaf
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