linux-kernel - Re: [PATCH] kvm: fix cpuid eax

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Message-ID: <4F9EF7FA.3060007@codemonkey.ws>
Date:	Mon, 30 Apr 2012 15:37:14 -0500
From:	Anthony Liguori <anthony@...emonkey.ws>
To:	"Michael S. Tsirkin" <mst@...hat.com>
CC:	Avi Kivity <avi@...hat.com>, Marcelo Tosatti <mtosatti@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org, davej@...hat.com
Subject: Re: [PATCH] kvm: fix cpuid eax

On 04/30/2012 09:39 AM, Michael S. Tsirkin wrote:
> cpuid eax should return the max leaf so that
> guests can find out the valid range.
> This matches Xen et al.

What KVM does here predates Xen and Hyper-V.

This is an ABI breaker.

Regards,

Anthony Liguori

>
> Tested using -cpu host.
>
> Signed-off-by: Michael S. Tsirkin<mst@...hat.com>
> ---
>   arch/x86/kvm/cpuid.c |    2 +-
>   1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 7d00d2d..bda4877 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -397,7 +397,7 @@ static int do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
>   	case KVM_CPUID_SIGNATURE: {
>   		char signature[12] = "KVMKVMKVM\0\0";
>   		u32 *sigptr = (u32 *)signature;
> -		entry->eax = 0;
> +		entry->eax = KVM_CPUID_FEATURES;
>   		entry->ebx = sigptr[0];
>   		entry->ecx = sigptr[1];
>   		entry->edx = sigptr[2];

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