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: <20130927151026.GA29416@aepfle.de>
Date:	Fri, 27 Sep 2013 17:10:26 +0200
From:	Olaf Hering <olaf@...fle.de>
To:	"K. Y. Srinivasan" <kys@...rosoft.com>
Cc:	x86@...nel.org, gregkh@...uxfoundation.org,
	linux-kernel@...r.kernel.org, devel@...uxdriverproject.org,
	apw@...onical.com, jasowang@...hat.com, tglx@...utronix.de,
	hpa@...or.com, 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 03, K. Y. Srinivasan wrote:

> Hyper-V supports a mechanism for retrieving the local APIC frequency.Use this and bypass
> the calibration code in the kernel. This would allow us to boot the Linux kernel as a
> "modern VM" on Hyper-V where many of the legacy devices (such as PIT) are not emulated.

> +	if (ms_hyperv.features & HV_X64_MSR_APIC_FREQUENCY_AVAILABLE) {
> +		/*
> +		 * Get the APIC frequency.
> +		 */
> +		rdmsrl(HV_X64_MSR_APIC_FREQUENCY, hv_lapic_frequency);
> +		hv_lapic_frequency /= HZ;

This leads to build errors on 32bit:

linux-3.12-rc2/arch/x86/kernel/cpu/mshyperv.c:88: undefined reference to `__udivdi3'

Up to now I have only tested on 64bit, sorry for that.


Olaf
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