KVM: x86: drop TSC offsetting kvm_x86_ops to fix KVM_GET/SET_CLOCK

Since commit a545ab6a0085 ("kvm: x86: add tsc_offset field to struct
kvm_vcpu_arch", 2016-09-07) the offset between host and L1 TSC is
cached and need not be fished out of the VMCS or VMCB.  This means
that we can implement adjust_tsc_offset_guest and read_l1_tsc
entirely in generic code.  The simplification is particularly
significant for VMX code, where vmx->nested.vmcs01_tsc_offset
was duplicating what is now in vcpu->arch.tsc_offset.  Therefore
the vmcs01_tsc_offset can be dropped completely.

More importantly, this fixes KVM_GET_CLOCK/KVM_SET_CLOCK
which, after commit 108b249c453d ("KVM: x86: introduce get_kvmclock_ns",
2016-09-01) called read_l1_tsc while the VMCS was not loaded.
It thus returned bogus values on Intel CPUs.

Fixes: 108b249c453dd7132599ab6dc7e435a7036c193f
Reported-by: Roman Kagan <rkagan@virtuozzo.com>
Reviewed-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 3 insertions, 36 deletions

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 74a4df993a51..754c3a7f444a 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -421,7 +421,6 @@ struct nested_vmx {
 	/* vmcs02_list cache of VMCSs recently used to run L2 guests */
 	struct list_head vmcs02_pool;
 	int vmcs02_num;
-	u64 vmcs01_tsc_offset;
 	bool change_vmcs01_virtual_x2apic_mode;
 	/* L2 must run next, and mustn't decide to exit to L1. */
 	bool nested_run_pending;
@@ -2605,20 +2604,6 @@ static u64 guest_read_tsc(struct kvm_vcpu *vcpu)
 }
 
 /*
- * Like guest_read_tsc, but always returns L1's notion of the timestamp
- * counter, even if a nested guest (L2) is currently running.
- */
-static u64 vmx_read_l1_tsc(struct kvm_vcpu *vcpu, u64 host_tsc)
-{
-	u64 tsc_offset;
-
-	tsc_offset = is_guest_mode(vcpu) ?
-		to_vmx(vcpu)->nested.vmcs01_tsc_offset :
-		vmcs_read64(TSC_OFFSET);
-	return host_tsc + tsc_offset;
-}
-
-/*
  * writes 'offset' into guest's timestamp counter offset register
  */
 static void vmx_write_tsc_offset(struct kvm_vcpu *vcpu, u64 offset)
@@ -2631,7 +2616,6 @@ static void vmx_write_tsc_offset(struct kvm_vcpu *vcpu, u64 offset)
 		 * to the newly set TSC to get L2's TSC.
 		 */
 		struct vmcs12 *vmcs12;
-		to_vmx(vcpu)->nested.vmcs01_tsc_offset = offset;
 		/* recalculate vmcs02.TSC_OFFSET: */
 		vmcs12 = get_vmcs12(vcpu);
 		vmcs_write64(TSC_OFFSET, offset +
@@ -2644,19 +2628,6 @@ static void vmx_write_tsc_offset(struct kvm_vcpu *vcpu, u64 offset)
 	}
 }
 
-static void vmx_adjust_tsc_offset_guest(struct kvm_vcpu *vcpu, s64 adjustment)
-{
-	u64 offset = vmcs_read64(TSC_OFFSET);
-
-	vmcs_write64(TSC_OFFSET, offset + adjustment);
-	if (is_guest_mode(vcpu)) {
-		/* Even when running L2, the adjustment needs to apply to L1 */
-		to_vmx(vcpu)->nested.vmcs01_tsc_offset += adjustment;
-	} else
-		trace_kvm_write_tsc_offset(vcpu->vcpu_id, offset,
-					   offset + adjustment);
-}
-
 static bool guest_cpuid_has_vmx(struct kvm_vcpu *vcpu)
 {
 	struct kvm_cpuid_entry2 *best = kvm_find_cpuid_entry(vcpu, 1, 0);
@@ -10061,9 +10032,9 @@ static void prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12)
 
 	if (vmcs12->cpu_based_vm_exec_control & CPU_BASED_USE_TSC_OFFSETING)
 		vmcs_write64(TSC_OFFSET,
-			vmx->nested.vmcs01_tsc_offset + vmcs12->tsc_offset);
+			vcpu->arch.tsc_offset + vmcs12->tsc_offset);
 	else
-		vmcs_write64(TSC_OFFSET, vmx->nested.vmcs01_tsc_offset);
+		vmcs_write64(TSC_OFFSET, vcpu->arch.tsc_offset);
 	if (kvm_has_tsc_control)
 		decache_tsc_multiplier(vmx);
 
@@ -10293,8 +10264,6 @@ static int nested_vmx_run(struct kvm_vcpu *vcpu, bool launch)
 
 	enter_guest_mode(vcpu);
 
-	vmx->nested.vmcs01_tsc_offset = vmcs_read64(TSC_OFFSET);
-
 	if (!(vmcs12->vm_entry_controls & VM_ENTRY_LOAD_DEBUG_CONTROLS))
 		vmx->nested.vmcs01_debugctl = vmcs_read64(GUEST_IA32_DEBUGCTL);
 
@@ -10818,7 +10787,7 @@ static void nested_vmx_vmexit(struct kvm_vcpu *vcpu, u32 exit_reason,
 	load_vmcs12_host_state(vcpu, vmcs12);
 
 	/* Update any VMCS fields that might have changed while L2 ran */
-	vmcs_write64(TSC_OFFSET, vmx->nested.vmcs01_tsc_offset);
+	vmcs_write64(TSC_OFFSET, vcpu->arch.tsc_offset);
 	if (vmx->hv_deadline_tsc == -1)
 		vmcs_clear_bits(PIN_BASED_VM_EXEC_CONTROL,
 				PIN_BASED_VMX_PREEMPTION_TIMER);
@@ -11339,8 +11308,6 @@ static struct kvm_x86_ops vmx_x86_ops __ro_after_init = {
 	.has_wbinvd_exit = cpu_has_vmx_wbinvd_exit,
 
 	.write_tsc_offset = vmx_write_tsc_offset,
-	.adjust_tsc_offset_guest = vmx_adjust_tsc_offset_guest,
-	.read_l1_tsc = vmx_read_l1_tsc,
 
 	.set_tdp_cr3 = vmx_set_cr3,