KVM: x86: Always write vCPU's current TSC offset/ratio in vendor hooks

Drop the @offset and @multiplier params from the kvm_x86_ops hooks for
propagating TSC offsets/multipliers into hardware, and instead have the
vendor implementations pull the information directly from the vCPU
structure.  The respective vCPU fields _must_ be written at the same
time in order to maintain consistent state, i.e. it's not random luck
that the value passed in by all callers is grabbed from the vCPU.

Explicitly grabbing the value from the vCPU field in SVM's implementation
in particular will allow for additional cleanup without introducing even
more subtle dependencies.  Specifically, SVM can skip the WRMSR if guest
state isn't loaded, i.e. svm_prepare_switch_to_guest() will load the
correct value for the vCPU prior to entering the guest.

This also reconciles KVM's handling of related values that are stored in
the vCPU, as svm_write_tsc_offset() already assumes/requires the caller
to have updated l1_tsc_offset.

Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Sean Christopherson <[email protected]>

Author: sean-jc

arch/x86/include/asm/kvm_host.h

@@ -1654,8 +1654,8 @@ struct kvm_x86_ops {
 
 	u64 (*get_l2_tsc_offset)(struct kvm_vcpu *vcpu);
 	u64 (*get_l2_tsc_multiplier)(struct kvm_vcpu *vcpu);
-	void (*write_tsc_offset)(struct kvm_vcpu *vcpu, u64 offset);
-	void (*write_tsc_multiplier)(struct kvm_vcpu *vcpu, u64 multiplier);
+	void (*write_tsc_offset)(struct kvm_vcpu *vcpu);
+	void (*write_tsc_multiplier)(struct kvm_vcpu *vcpu);
 
 	/*
 	 * Retrieve somewhat arbitrary exit information.  Intended to

arch/x86/kvm/svm/nested.c

@@ -1103,7 +1103,7 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
 	if (kvm_caps.has_tsc_control &&
 	    vcpu->arch.tsc_scaling_ratio != vcpu->arch.l1_tsc_scaling_ratio) {
 		vcpu->arch.tsc_scaling_ratio = vcpu->arch.l1_tsc_scaling_ratio;
-		svm_write_tsc_multiplier(vcpu, vcpu->arch.tsc_scaling_ratio);
+		svm_write_tsc_multiplier(vcpu);
 	}
 
 	svm->nested.ctl.nested_cr3 = 0;
@@ -1536,7 +1536,7 @@ void nested_svm_update_tsc_ratio_msr(struct kvm_vcpu *vcpu)
 	vcpu->arch.tsc_scaling_ratio =
 		kvm_calc_nested_tsc_multiplier(vcpu->arch.l1_tsc_scaling_ratio,
 					       svm->tsc_ratio_msr);
-	svm_write_tsc_multiplier(vcpu, vcpu->arch.tsc_scaling_ratio);
+	svm_write_tsc_multiplier(vcpu);
 }
 
 /* Inverse operation of nested_copy_vmcb_control_to_cache(). asid is copied too. */

arch/x86/kvm/svm/svm.c

@@ -1137,19 +1137,19 @@ static u64 svm_get_l2_tsc_multiplier(struct kvm_vcpu *vcpu)
 	return svm->tsc_ratio_msr;
 }
 
-static void svm_write_tsc_offset(struct kvm_vcpu *vcpu, u64 offset)
+static void svm_write_tsc_offset(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
 
 	svm->vmcb01.ptr->control.tsc_offset = vcpu->arch.l1_tsc_offset;
-	svm->vmcb->control.tsc_offset = offset;
+	svm->vmcb->control.tsc_offset = vcpu->arch.tsc_offset;
 	vmcb_mark_dirty(svm->vmcb, VMCB_INTERCEPTS);
 }
 
-void svm_write_tsc_multiplier(struct kvm_vcpu *vcpu, u64 multiplier)
+void svm_write_tsc_multiplier(struct kvm_vcpu *vcpu)
 {
 	preempt_disable();
-	__svm_write_tsc_multiplier(multiplier);
+	__svm_write_tsc_multiplier(vcpu->arch.tsc_scaling_ratio);
 	preempt_enable();
 }
 

arch/x86/kvm/svm/svm.h

@@ -658,7 +658,7 @@ int nested_svm_check_exception(struct vcpu_svm *svm, unsigned nr,
 			       bool has_error_code, u32 error_code);
 int nested_svm_exit_special(struct vcpu_svm *svm);
 void nested_svm_update_tsc_ratio_msr(struct kvm_vcpu *vcpu);
-void svm_write_tsc_multiplier(struct kvm_vcpu *vcpu, u64 multiplier);
+void svm_write_tsc_multiplier(struct kvm_vcpu *vcpu);
 void nested_copy_vmcb_control_to_cache(struct vcpu_svm *svm,
 				       struct vmcb_control_area *control);
 void nested_copy_vmcb_save_to_cache(struct vcpu_svm *svm,

arch/x86/kvm/vmx/vmx.c

@@ -1898,14 +1898,14 @@ u64 vmx_get_l2_tsc_multiplier(struct kvm_vcpu *vcpu)
 	return kvm_caps.default_tsc_scaling_ratio;
 }
 
-static void vmx_write_tsc_offset(struct kvm_vcpu *vcpu, u64 offset)
+static void vmx_write_tsc_offset(struct kvm_vcpu *vcpu)
 {
-	vmcs_write64(TSC_OFFSET, offset);
+	vmcs_write64(TSC_OFFSET, vcpu->arch.tsc_offset);
 }
 
-static void vmx_write_tsc_multiplier(struct kvm_vcpu *vcpu, u64 multiplier)
+static void vmx_write_tsc_multiplier(struct kvm_vcpu *vcpu)
 {
-	vmcs_write64(TSC_MULTIPLIER, multiplier);
+	vmcs_write64(TSC_MULTIPLIER, vcpu->arch.tsc_scaling_ratio);
 }
 
 /*

arch/x86/kvm/x86.c

@@ -2613,7 +2613,7 @@ static void kvm_vcpu_write_tsc_offset(struct kvm_vcpu *vcpu, u64 l1_offset)
 	else
 		vcpu->arch.tsc_offset = l1_offset;
 
-	static_call(kvm_x86_write_tsc_offset)(vcpu, vcpu->arch.tsc_offset);
+	static_call(kvm_x86_write_tsc_offset)(vcpu);
 }
 
 static void kvm_vcpu_write_tsc_multiplier(struct kvm_vcpu *vcpu, u64 l1_multiplier)
@@ -2629,8 +2629,7 @@ static void kvm_vcpu_write_tsc_multiplier(struct kvm_vcpu *vcpu, u64 l1_multipli
 		vcpu->arch.tsc_scaling_ratio = l1_multiplier;
 
 	if (kvm_caps.has_tsc_control)
-		static_call(kvm_x86_write_tsc_multiplier)(
-			vcpu, vcpu->arch.tsc_scaling_ratio);
+		static_call(kvm_x86_write_tsc_multiplier)(vcpu);
 }
 
 static inline bool kvm_check_tsc_unstable(void)