Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756689Ab0D0SMx (ORCPT ); Tue, 27 Apr 2010 14:12:53 -0400 Received: from mx1.redhat.com ([209.132.183.28]:28027 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752157Ab0D0SMv (ORCPT ); Tue, 27 Apr 2010 14:12:51 -0400 Message-ID: <4BD7291F.6010809@redhat.com> Date: Tue, 27 Apr 2010 21:12:47 +0300 From: Avi Kivity User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.9) Gecko/20100330 Fedora/3.0.4-1.fc12 Thunderbird/3.0.4 MIME-Version: 1.0 To: Glauber Costa CC: kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 4/6] export new cpuid KVM_CAP References: <1272303988-21929-1-git-send-email-glommer@redhat.com> <1272303988-21929-2-git-send-email-glommer@redhat.com> <1272303988-21929-3-git-send-email-glommer@redhat.com> <1272303988-21929-4-git-send-email-glommer@redhat.com> <1272303988-21929-5-git-send-email-glommer@redhat.com> In-Reply-To: <1272303988-21929-5-git-send-email-glommer@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2604 Lines: 70 On 04/26/2010 08:46 PM, 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 > --- > 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 > Please document this in Documentation/kvm/cpuid.txt (also /msr.txt). > > #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) | > + (1<< KVM_FEATURE_CLOCKSOURCE2); > + break; > default: > r = 0; > break; > Hmm. We already have an API to get cpuid bits: KVM_GET_SUPPORTED_CPUID2. The nice thing about it is that it will mean -cpu host will work out of the box. -- Do not meddle in the internals of kernels, for they are subtle and quick to panic. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/