Messages in this thread | | | Date | Tue, 27 Apr 2010 21:12:47 +0300 | From | Avi Kivity <> | Subject | Re: [PATCH 4/6] export new cpuid KVM_CAP |
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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<glommer@redhat.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 >
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.
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