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KVM: Don't automatically expose the TSC deadline timer in cpuid

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Unlike all of the other cpuid bits, the TSC deadline timer bit is set
unconditionally, regardless of what userspace wants.

This is broken in several ways:
 - if userspace doesn't use KVM_CREATE_IRQCHIP, and doesn't emulate the TSC
   deadline timer feature, a guest that uses the feature will break
 - live migration to older host kernels that don't support the TSC deadline
   timer will cause the feature to be pulled from under the guest's feet;
   breaking it
 - guests that are broken wrt the feature will fail.

Fix by not enabling the feature automatically; instead report it to userspace.
Because the feature depends on KVM_CREATE_IRQCHIP, which we cannot guarantee
will be called, we expose it via a KVM_CAP_TSC_DEADLINE_TIMER and not
KVM_GET_SUPPORTED_CPUID.

Fixes the Illumos guest kernel, which uses the TSC deadline timer feature.

[avi: add the KVM_CAP + documentation]

Reported-by: Alexey Zaytsev <alexey.zaytsev@gmail.com>
Tested-by: Alexey Zaytsev <alexey.zaytsev@gmail.com>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
This commit is contained in:
Jan Kiszka 2011-12-21 12:28:29 +01:00 committed by Avi Kivity
parent 3d27e23b17
commit 4d25a066b6
3 changed files with 19 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
Documentation/virtual/kvm/api.txt
View File

@ -1100,6 +1100,15 @@ emulate them efficiently. The fields in each entry are defined as follows:
eax, ebx, ecx, edx: the values returned by the cpuid instruction for
this function/index combination
The TSC deadline timer feature (CPUID leaf 1, ecx[24]) is always returned
as false, since the feature depends on KVM_CREATE_IRQCHIP for local APIC
support. Instead it is reported via
ioctl(KVM_CHECK_EXTENSION, KVM_CAP_TSC_DEADLINE_TIMER)
if that returns true and you use KVM_CREATE_IRQCHIP, or if you emulate the
feature in userspace, then you can enable the feature for KVM_SET_CPUID2.
4.47 KVM_PPC_GET_PVINFO
Capability: KVM_CAP_PPC_GET_PVINFO

19
arch/x86/kvm/x86.c
View File

@ -602,7 +602,6 @@ static void update_cpuid(struct kvm_vcpu *vcpu)
{
struct kvm_cpuid_entry2 *best;
struct kvm_lapic *apic = vcpu->arch.apic;
u32 timer_mode_mask;
best = kvm_find_cpuid_entry(vcpu, 1, 0);
if (!best)
@ -615,15 +614,12 @@ static void update_cpuid(struct kvm_vcpu *vcpu)
best->ecx |= bit(X86_FEATURE_OSXSAVE);
}
if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL &&
best->function == 0x1) {
best->ecx |= bit(X86_FEATURE_TSC_DEADLINE_TIMER);
timer_mode_mask = 3 << 17;
} else
timer_mode_mask = 1 << 17;
if (apic)
apic->lapic_timer.timer_mode_mask = timer_mode_mask;
if (apic) {
if (best->ecx & bit(X86_FEATURE_TSC_DEADLINE_TIMER))
apic->lapic_timer.timer_mode_mask = 3 << 17;
else
apic->lapic_timer.timer_mode_mask = 1 << 17;
}
}
int kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
@ -2135,6 +2131,9 @@ int kvm_dev_ioctl_check_extension(long ext)
case KVM_CAP_TSC_CONTROL:
r = kvm_has_tsc_control;
break;
case KVM_CAP_TSC_DEADLINE_TIMER:
r = boot_cpu_has(X86_FEATURE_TSC_DEADLINE_TIMER);
break;
default:
r = 0;
break;

1
include/linux/kvm.h
View File

@ -557,6 +557,7 @@ struct kvm_ppc_pvinfo {
#define KVM_CAP_MAX_VCPUS 66 /* returns max vcpus per vm */
#define KVM_CAP_PPC_PAPR 68
#define KVM_CAP_S390_GMAP 71
#define KVM_CAP_TSC_DEADLINE_TIMER 72
#ifdef KVM_CAP_IRQ_ROUTING