On Mon, Aug 13, 2018 at 09:31:42AM -0700, Drew Schmitt wrote:
> On Mon, Aug 13, 2018 at 6:50 AM Konrad Rzeszutek Wilk
> <konrad.wilk@xxxxxxxxxx> wrote:
> >
> > On Fri, Aug 10, 2018 at 02:26:03PM -0700, Drew Schmitt wrote:
> > > Add KVM_CAP_MSR_PLATFORM_INFO so that userspace can disable guest access
> > > to reads of MSR_PLATFORM_INFO.
> >
> > Or enable it - by default it is enabled. Perhaps by default it should
> > be disabled?
>
> We wanted to make this an opt-out functionality in order to not change
> the current default behavior (which today is a guest *can* read this
> MSR).
<nods> What is the danger of disabling access to this in the first place?
Or providing by default some cooked up value ? Does it break Windows? Linux guests?
>
> >
> >
> > Also shouldn't there be an update to the API docs?
>
> Yes, added in v2.
>
> >
> > >
> > > Signed-off-by: Drew Schmitt <dasch@xxxxxxxxxx>
> > > ---
> > > arch/x86/include/asm/kvm_host.h | 2 ++
> > > arch/x86/kvm/x86.c | 10 ++++++++++
> > > include/uapi/linux/kvm.h | 1 +
> > > 3 files changed, 13 insertions(+)
> > >
> > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > > index c13cd28d9d1be..c0497c7a4869f 100644
> > > --- a/arch/x86/include/asm/kvm_host.h
> > > +++ b/arch/x86/include/asm/kvm_host.h
> > > @@ -853,6 +853,8 @@ struct kvm_arch {
> > >
> > > bool x2apic_format;
> > > bool x2apic_broadcast_quirk_disabled;
> > > +
> > > + bool guest_can_read_msr_platform_info;
> > > };
> > >
> > > struct kvm_vm_stat {
> > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > > index 0278cde1893ca..b27d88fc6eb8f 100644
> > > --- a/arch/x86/kvm/x86.c
> > > +++ b/arch/x86/kvm/x86.c
> > > @@ -2743,6 +2743,9 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> > > msr_info->data = vcpu->arch.osvw.status;
> > > break;
> > > case MSR_PLATFORM_INFO:
> > > + if (!msr_info->host_initiated &&
> > > + !vcpu->kvm->arch.guest_can_read_msr_platform_info)
> > > + return 1;
> > > msr_info->data = vcpu->arch.msr_platform_info;
> > > break;
> > > case MSR_MISC_FEATURES_ENABLES:
> > > @@ -2890,6 +2893,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
> > > case KVM_CAP_SPLIT_IRQCHIP:
> > > case KVM_CAP_IMMEDIATE_EXIT:
> > > case KVM_CAP_GET_MSR_FEATURES:
> > > + case KVM_CAP_MSR_PLATFORM_INFO:
> > > r = 1;
> > > break;
> > > case KVM_CAP_SYNC_REGS:
> > > @@ -4259,6 +4263,10 @@ static int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
> > > kvm->arch.pause_in_guest = true;
> > > r = 0;
> > > break;
> > > + case KVM_CAP_MSR_PLATFORM_INFO:
> > > + kvm->arch.guest_can_read_msr_platform_info = cap->args[0];
> > > + r = 0;
> > > + break;
> > > default:
> > > r = -EINVAL;
> > > break;
> > > @@ -8724,6 +8732,8 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
> > > kvm->arch.kvmclock_offset = -ktime_get_boot_ns();
> > > pvclock_update_vm_gtod_copy(kvm);
> > >
> > > + kvm->arch.guest_can_read_msr_platform_info = true;
> > > +
> > > INIT_DELAYED_WORK(&kvm->arch.kvmclock_update_work, kvmclock_update_fn);
> > > INIT_DELAYED_WORK(&kvm->arch.kvmclock_sync_work, kvmclock_sync_fn);
> > >
> > > diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> > > index b6270a3b38e9f..f3367041b609b 100644
> > > --- a/include/uapi/linux/kvm.h
> > > +++ b/include/uapi/linux/kvm.h
> > > @@ -949,6 +949,7 @@ struct kvm_ppc_resize_hpt {
> > > #define KVM_CAP_GET_MSR_FEATURES 153
> > > #define KVM_CAP_HYPERV_EVENTFD 154
> > > #define KVM_CAP_HYPERV_TLBFLUSH 155
> > > +#define KVM_CAP_MSR_PLATFORM_INFO 156
> > >
> > > #ifdef KVM_CAP_IRQ_ROUTING
> > >
> > > --
> > > 2.18.0.597.ga71716f1ad-goog
> > >
