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SubjectRe: [PATCH 4/6] export new cpuid KVM_CAP
On Tue, Apr 27, 2010 at 10:30:48AM -0300, Marcelo Tosatti wrote:
> 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@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
> >
> > #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.

Ok, sorry. My bad here.

at a quick glance, I did not realize you were commenting on this
patch specifically. KVM_CAP_X86_CPUID_FEATURE_LIST is a new
entity, so there is no need to return a deprecated feature.

I will remove that.



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