KVM: x86: Save L1 TSC offset in 'struct kvm_vcpu_arch'

Save L1's TSC offset in 'struct kvm_vcpu_arch' and drop the kvm_x86_ops
hook read_l1_tsc_offset().  This avoids a retpoline (when configured)
when reading L1's effective TSC, which is done at least once on every
VM-Exit.

No functional change intended.
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20200502043234.12481-2-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/kvm_host.h

@@ -708,6 +708,7 @@ struct kvm_vcpu_arch {
 		struct gfn_to_pfn_cache cache;
 	} st;
 
+	u64 l1_tsc_offset;
 	u64 tsc_offset;
 	u64 last_guest_tsc;
 	u64 last_host_tsc;
@@ -1165,7 +1166,6 @@ struct kvm_x86_ops {
 
 	bool (*has_wbinvd_exit)(void);
 
-	u64 (*read_l1_tsc_offset)(struct kvm_vcpu *vcpu);
 	/* Returns actual tsc_offset set in active VMCS */
 	u64 (*write_l1_tsc_offset)(struct kvm_vcpu *vcpu, u64 offset);
 

arch/x86/kvm/svm/svm.c

@@ -951,16 +951,6 @@ static void init_sys_seg(struct vmcb_seg *seg, uint32_t type)
 	seg->base = 0;
 }
 
-static u64 svm_read_l1_tsc_offset(struct kvm_vcpu *vcpu)
-{
-	struct vcpu_svm *svm = to_svm(vcpu);
-
-	if (is_guest_mode(vcpu))
-		return svm->nested.hsave->control.tsc_offset;
-
-	return vcpu->arch.tsc_offset;
-}
-
 static u64 svm_write_l1_tsc_offset(struct kvm_vcpu *vcpu, u64 offset)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
@@ -4075,7 +4065,6 @@ static struct kvm_x86_ops svm_x86_ops __initdata = {
 
 	.has_wbinvd_exit = svm_has_wbinvd_exit,
 
-	.read_l1_tsc_offset = svm_read_l1_tsc_offset,
 	.write_l1_tsc_offset = svm_write_l1_tsc_offset,
 
 	.load_mmu_pgd = svm_load_mmu_pgd,

arch/x86/kvm/vmx/vmx.c

@@ -1740,17 +1740,6 @@ static void setup_msrs(struct vcpu_vmx *vmx)
 		vmx_update_msr_bitmap(&vmx->vcpu);
 }
 
-static u64 vmx_read_l1_tsc_offset(struct kvm_vcpu *vcpu)
-{
-	struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
-
-	if (is_guest_mode(vcpu) &&
-	    (vmcs12->cpu_based_vm_exec_control & CPU_BASED_USE_TSC_OFFSETTING))
-		return vcpu->arch.tsc_offset - vmcs12->tsc_offset;
-
-	return vcpu->arch.tsc_offset;
-}
-
 static u64 vmx_write_l1_tsc_offset(struct kvm_vcpu *vcpu, u64 offset)
 {
 	struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
@@ -7881,7 +7870,6 @@ static struct kvm_x86_ops vmx_x86_ops __initdata = {
 
 	.has_wbinvd_exit = cpu_has_vmx_wbinvd_exit,
 
-	.read_l1_tsc_offset = vmx_read_l1_tsc_offset,
 	.write_l1_tsc_offset = vmx_write_l1_tsc_offset,
 
 	.load_mmu_pgd = vmx_load_mmu_pgd,

arch/x86/kvm/x86.c

@@ -1910,7 +1910,7 @@ static void kvm_track_tsc_matching(struct kvm_vcpu *vcpu)
 
 static void update_ia32_tsc_adjust_msr(struct kvm_vcpu *vcpu, s64 offset)
 {
-	u64 curr_offset = kvm_x86_ops.read_l1_tsc_offset(vcpu);
+	u64 curr_offset = vcpu->arch.l1_tsc_offset;
 	vcpu->arch.ia32_tsc_adjust_msr += offset - curr_offset;
 }
 
@@ -1952,14 +1952,13 @@ static u64 kvm_compute_tsc_offset(struct kvm_vcpu *vcpu, u64 target_tsc)
 
 u64 kvm_read_l1_tsc(struct kvm_vcpu *vcpu, u64 host_tsc)
 {
-	u64 tsc_offset = kvm_x86_ops.read_l1_tsc_offset(vcpu);
-
-	return tsc_offset + kvm_scale_tsc(vcpu, host_tsc);
+	return vcpu->arch.l1_tsc_offset + kvm_scale_tsc(vcpu, host_tsc);
 }
 EXPORT_SYMBOL_GPL(kvm_read_l1_tsc);
 
 static void kvm_vcpu_write_tsc_offset(struct kvm_vcpu *vcpu, u64 offset)
 {
+	vcpu->arch.l1_tsc_offset = offset;
 	vcpu->arch.tsc_offset = kvm_x86_ops.write_l1_tsc_offset(vcpu, offset);
 }
 
@@ -2084,7 +2083,7 @@ EXPORT_SYMBOL_GPL(kvm_write_tsc);
 static inline void adjust_tsc_offset_guest(struct kvm_vcpu *vcpu,
 					   s64 adjustment)
 {
-	u64 tsc_offset = kvm_x86_ops.read_l1_tsc_offset(vcpu);
+	u64 tsc_offset = vcpu->arch.l1_tsc_offset;
 	kvm_vcpu_write_tsc_offset(vcpu, tsc_offset + adjustment);
 }