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>

1 files changed, 4 insertions, 4 deletions

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index ea8f9f03e92..6b37f18a166 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1098,7 +1098,7 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
 
         /* 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 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
                 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 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
 {
         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 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
         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();