From mboxrd@z Thu Jan  1 00:00:00 1970
From: Avi Kivity <avi@redhat.com>
Subject: Re: [PATCH] Emulate MSR_EBC_FREQUENCY_ID
Date: Thu, 09 Sep 2010 11:12:42 +0300
Message-ID: <4C8896FA.1040103@redhat.com>
References: <1284017626-30542-1-git-send-email-Jes.Sorensen@redhat.com>
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To: Jes.Sorensen@redhat.com
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  On 09/09/2010 10:33 AM, Jes.Sorensen@redhat.com wrote:
> From: Jes Sorensen<Jes.Sorensen@redhat.com>
>
> Some operating systems store data about the host processor at the
> time of installation, and when booted on a more uptodate cpu tries
> to read MSR_EBC_FREQUENCY_ID. This has been found with XP.
>
>
> index f47db25..78fa8a0 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1641,6 +1641,14 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata)
>   	case MSR_K8_INT_PENDING_MSG:
>   	case MSR_AMD64_NB_CFG:
>   	case MSR_FAM10H_MMIO_CONF_BASE:
> +		/*
> +		 * MSR_EBC_FREQUENCY_ID
> +		 * Conservative value valid for even the basic CPU models.
> +		 * Models 0,1: 000 in bits 23:21 indicating a bus speed of
> +		 * 100MHz, model 2 000 in bits 18:16 indicating 100MHz,
> +		 * and 266MHz for model 3, or 4.
> +		 */
> +	case MSR_EBC_FREQUENCY_ID:
>   		data = 0;
>   		break;
>   	case MSR_MTRRcap:

 From the spec:

> 31:24 Core Clock Frequency to System
>       Bus Frequency Ratio. (R)
>       The processor core clock
>       frequency to system bus
>       frequency ratio observed at the
>       de-assertion of the reset pin.

A frequency ratio of 0 might be unexpected by some guests.


-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.