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KVM: x86: Control guest reads of MSR_PLATFORM_INFO

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Add KVM_CAP_MSR_PLATFORM_INFO so that userspace can disable guest access
to reads of MSR_PLATFORM_INFO.

Disabling access to reads of this MSR gives userspace the control to "expose"
this platform-dependent information to guests in a clear way. As it exists
today, guests that read this MSR would get unpopulated information if userspace
hadn't already set it (and prior to this patch series, only the CPUID faulting
information could have been populated). This existing interface could be
confusing if guests don't handle the potential for incorrect/incomplete
information gracefully (e.g. zero reported for base frequency).

Signed-off-by: Drew Schmitt <dasch@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Drew Schmitt
2018-08-20 10:32:15 -07:00
committed by Paolo Bonzini
parent d84f1cff90
commit 6fbbde9a19
4 changed files with 22 additions and 0 deletions
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10
arch/x86/kvm/x86.c
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@@ -2779,6 +2779,9 @@ 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:
@@ -2926,6 +2929,7 @@ 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:
@@ -4349,6 +4353,10 @@ split_irqchip_unlock:
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;
@@ -8857,6 +8865,8 @@ 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);