KVM: L1 TSC handling
KVM assumed in several places that reading the TSC MSR returns the value for
L1. This is incorrect, because when L2 is running, the correct TSC read exit
emulation is to return L2's value.
We therefore add a new x86_ops function, read_l1_tsc, to use in places that
specifically need to read the L1 TSC, NOT the TSC of the current level of
guest.
Note that one change, of one line in kvm_arch_vcpu_load, is made redundant
by a different patch sent by Zachary Amsden (and not yet applied):
kvm_arch_vcpu_load() should not read the guest TSC, and if it didn't, of
course we didn't have to change the call of kvm_get_msr() to read_l1_tsc().
[avi: moved callback to kvm_x86_ops tsc block]
Signed-off-by: Nadav Har'El <nyh@il.ibm.com>
Acked-by: Zachary Amsdem <zamsden@gmail.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index b31a341..6ab4241 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -630,6 +630,7 @@
void (*write_tsc_offset)(struct kvm_vcpu *vcpu, u64 offset);
u64 (*compute_tsc_offset)(struct kvm_vcpu *vcpu, u64 target_tsc);
+ u64 (*read_l1_tsc)(struct kvm_vcpu *vcpu);
void (*get_exit_info)(struct kvm_vcpu *vcpu, u64 *info1, u64 *info2);
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index f043168..590d1d2 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -2910,6 +2910,13 @@
return 0;
}
+u64 svm_read_l1_tsc(struct kvm_vcpu *vcpu)
+{
+ struct vmcb *vmcb = get_host_vmcb(to_svm(vcpu));
+ return vmcb->control.tsc_offset +
+ svm_scale_tsc(vcpu, native_read_tsc());
+}
+
static int svm_get_msr(struct kvm_vcpu *vcpu, unsigned ecx, u64 *data)
{
struct vcpu_svm *svm = to_svm(vcpu);
@@ -4201,6 +4208,7 @@
.write_tsc_offset = svm_write_tsc_offset,
.adjust_tsc_offset = svm_adjust_tsc_offset,
.compute_tsc_offset = svm_compute_tsc_offset,
+ .read_l1_tsc = svm_read_l1_tsc,
.set_tdp_cr3 = set_tdp_cr3,
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 03df703..97b6454 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -1748,6 +1748,21 @@
}
/*
+ * Like guest_read_tsc, but always returns L1's notion of the timestamp
+ * counter, even if a nested guest (L2) is currently running.
+ */
+u64 vmx_read_l1_tsc(struct kvm_vcpu *vcpu)
+{
+ u64 host_tsc, tsc_offset;
+
+ rdtscll(host_tsc);
+ tsc_offset = is_guest_mode(vcpu) ?
+ to_vmx(vcpu)->nested.vmcs01_tsc_offset :
+ vmcs_read64(TSC_OFFSET);
+ return host_tsc + tsc_offset;
+}
+
+/*
* Empty call-back. Needs to be implemented when VMX enables the SET_TSC_KHZ
* ioctl. In this case the call-back should update internal vmx state to make
* the changes effective.
@@ -7010,6 +7025,7 @@
.write_tsc_offset = vmx_write_tsc_offset,
.adjust_tsc_offset = vmx_adjust_tsc_offset,
.compute_tsc_offset = vmx_compute_tsc_offset,
+ .read_l1_tsc = vmx_read_l1_tsc,
.set_tdp_cr3 = vmx_set_cr3,
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index ea8f9f0..6b37f18 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1098,7 +1098,7 @@
/* Keep irq disabled to prevent changes to the clock */
local_irq_save(flags);
- kvm_get_msr(v, MSR_IA32_TSC, &tsc_timestamp);
+ tsc_timestamp = kvm_x86_ops->read_l1_tsc(v);
kernel_ns = get_kernel_ns();
this_tsc_khz = vcpu_tsc_khz(v);
if (unlikely(this_tsc_khz == 0)) {
@@ -2218,7 +2218,7 @@
s64 tsc_delta;
u64 tsc;
- kvm_get_msr(vcpu, MSR_IA32_TSC, &tsc);
+ tsc = kvm_x86_ops->read_l1_tsc(vcpu);
tsc_delta = !vcpu->arch.last_guest_tsc ? 0 :
tsc - vcpu->arch.last_guest_tsc;
@@ -2242,7 +2242,7 @@
{
kvm_x86_ops->vcpu_put(vcpu);
kvm_put_guest_fpu(vcpu);
- kvm_get_msr(vcpu, MSR_IA32_TSC, &vcpu->arch.last_guest_tsc);
+ vcpu->arch.last_guest_tsc = kvm_x86_ops->read_l1_tsc(vcpu);
}
static int is_efer_nx(void)
@@ -5729,7 +5729,7 @@
if (hw_breakpoint_active())
hw_breakpoint_restore();
- kvm_get_msr(vcpu, MSR_IA32_TSC, &vcpu->arch.last_guest_tsc);
+ vcpu->arch.last_guest_tsc = kvm_x86_ops->read_l1_tsc(vcpu);
vcpu->mode = OUTSIDE_GUEST_MODE;
smp_wmb();
