linux-kernel - Re: [PATCH 4/6] export new cpuid KVM

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Message-ID: <20100427133048.GC18410@amt.cnet>
Date:	Tue, 27 Apr 2010 10:30:48 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Glauber Costa <glommer@...hat.com>
Cc:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org, avi@...hat.com
Subject: Re: [PATCH 4/6] export new cpuid KVM_CAP

On Mon, Apr 26, 2010 at 01:46:26PM -0400, Glauber Costa wrote:
> Since we're changing the msrs kvmclock uses, we have to communicate
> that to the guest, through cpuid. We can add a new KVM_CAP to the
> hypervisor, and then patch userspace to recognize it.
> 
> And if we ever add a new cpuid bit in the future, we have to do that again,
> which create some complexity and delay in feature adoption.
> 
> Instead, what I'm proposing in this patch is a new capability, called
> KVM_CAP_X86_CPUID_FEATURE_LIST, that returns the current feature list
> currently supported by the hypervisor. If we ever want to add or remove
> some feature, we only need to tweak into the HV, leaving userspace untouched.
> 
> Signed-off-by: Glauber Costa <glommer@...hat.com>
> ---
>  arch/x86/include/asm/kvm_para.h |    4 ++++
>  arch/x86/kvm/x86.c              |    6 ++++++
>  include/linux/kvm.h             |    1 +
>  3 files changed, 11 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
> index 9734808..f019f8c 100644
> --- a/arch/x86/include/asm/kvm_para.h
> +++ b/arch/x86/include/asm/kvm_para.h
> @@ -16,6 +16,10 @@
>  #define KVM_FEATURE_CLOCKSOURCE		0
>  #define KVM_FEATURE_NOP_IO_DELAY	1
>  #define KVM_FEATURE_MMU_OP		2
> +/* This indicates that the new set of kvmclock msrs
> + * are available. The use of 0x11 and 0x12 is deprecated
> + */
> +#define KVM_FEATURE_CLOCKSOURCE2        3
>  
>  #define MSR_KVM_WALL_CLOCK  0x11
>  #define MSR_KVM_SYSTEM_TIME 0x12
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index a2ead7f..04f04aa 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1545,6 +1545,12 @@ int kvm_dev_ioctl_check_extension(long ext)
>  	case KVM_CAP_MCE:
>  		r = KVM_MAX_MCE_BANKS;
>  		break;
> +	case KVM_CAP_X86_CPUID_FEATURE_LIST:
> +		r = (1 << KVM_FEATURE_CLOCKSOURCE) |
> +		(1 << KVM_FEATURE_NOP_IO_DELAY) |
> +		(1 << KVM_FEATURE_MMU_OP) |

Remove this flag, it has been deprecated.

> +		(1 << KVM_FEATURE_CLOCKSOURCE2);
> +		break;
>  	default:

Also missing qemu-kvm/qemu patches.

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