Date: Fri, 27 Sep 2013 17:10:26 +0200
From: Olaf Hering <olaf@aepfle.de>
To: "K. Y. Srinivasan" <kys@microsoft.com>
Cc: x86@kernel.org, gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org,
        devel@linuxdriverproject.org, apw@canonical.com, jasowang@redhat.com,
        tglx@linutronix.de, hpa@zytor.com, JBeulich@suse.com, bp@alien8.de
Subject: Re: [PATCH V2 1/1] X86: Hyper-V: Get the local APIC timer frequency
 from the hypervisor
Message-ID: <20130927151026.GA29416@aepfle.de>
References: <1378233023-4512-1-git-send-email-kys@microsoft.com>
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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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