linux-kernel - RE: [PATCH V2 1/1] X86: Hyper-V: Get the local APIC timer frequency from the hypervisor

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Message-ID: <2d39849c011b4cc794686a41e45db87a@SN2PR03MB061.namprd03.prod.outlook.com>
Date:	Mon, 23 Sep 2013 13:02:42 +0000
From:	KY Srinivasan <kys@...rosoft.com>
To:	Gleb Natapov <gleb@...hat.com>
CC:	"H. Peter Anvin" <hpa@...or.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	"olaf@...fle.de" <olaf@...fle.de>,
	"apw@...onical.com" <apw@...onical.com>,
	"jasowang@...hat.com" <jasowang@...hat.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"JBeulich@...e.com" <JBeulich@...e.com>,
	"bp@...en8.de" <bp@...en8.de>,
	"dmitry.torokhov@...il.com" <dmitry.torokhov@...il.com>
Subject: RE: [PATCH V2 1/1] X86: Hyper-V: Get the local APIC timer frequency
 from the hypervisor



> -----Original Message-----
> From: Gleb Natapov [mailto:gleb@...hat.com]
> Sent: Tuesday, September 17, 2013 10:44 PM
> To: KY Srinivasan
> Cc: H. Peter Anvin; x86@...nel.org; gregkh@...uxfoundation.org; linux-
> kernel@...r.kernel.org; devel@...uxdriverproject.org; olaf@...fle.de;
> apw@...onical.com; jasowang@...hat.com; tglx@...utronix.de;
> JBeulich@...e.com; bp@...en8.de
> Subject: Re: [PATCH V2 1/1] X86: Hyper-V: Get the local APIC timer frequency
> from the hypervisor
> 
> On Tue, Sep 17, 2013 at 07:53:36PM +0000, KY Srinivasan wrote:
> > > > Thanks Gleb. Here is the link for the latest Hyper-V specification:
> > > > http://www.microsoft.com/en-us/download/details.aspx?id=39289
> > > >
> > > > This spec talks about how migration is handled with regards to TSC.
> > > >
> > > All I can see is "15.4.3 Partition Reference TSC Mechanism". I see
> > > nothing about HV_X64_MSR_TSC_FREQUENCY specifically. To access this MSR
> > > a partition needs AccessFrequencyMsrs privilege, may be partition that
> > > cab be migrated does not have this privilege?
> >
> > If you use the MSR to read the TSC frequency, then indeed when you migrate
> then there
> > is no guarantee that the TSC frequency won't change when you migrate. The
> approach
> > described in section 15.4.3 is the preferred approach that can accommodate
> migration.
> >
> Thanks.

Peter,
Please let me know if there are other issues I need to address here. Now that Dmitry has queued up the
Hyper-V keyboard driver, with this patch we can fully support Linux on our uefi firmware.

Regards,

K. Y 
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