KVM: nSVM: Move TLB flushing logic (or lack thereof) to dedicated helper

Introduce nested_svm_transition_tlb_flush() and use it force an MMU sync
and TLB flush on nSVM VM-Enter and VM-Exit instead of sneaking the logic
into the __kvm_mmu_new_pgd() call sites.  Add a partial todo list to
document issues that need to be addressed before the unconditional sync
and flush can be modified to look more like nVMX's logic.

In addition to making nSVM's forced flushing more overt (guess who keeps
losing track of it), the new helper brings further convergence between
nSVM and nVMX, and also sets the stage for dropping the "skip" params
from __kvm_mmu_new_pgd().

Cc: Maxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210609234235.1244004-7-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/mmu/mmu.c

@@ -4684,7 +4684,7 @@ void kvm_init_shadow_npt_mmu(struct kvm_vcpu *vcpu, u32 cr0, u32 cr4, u32 efer,
 	struct kvm_mmu *context = &vcpu->arch.guest_mmu;
 	union kvm_mmu_role new_role = kvm_calc_shadow_npt_root_page_role(vcpu);
 
-	__kvm_mmu_new_pgd(vcpu, nested_cr3, new_role.base, false, false);
+	__kvm_mmu_new_pgd(vcpu, nested_cr3, new_role.base, true, true);
 
 	if (new_role.as_u64 != context->mmu_role.as_u64) {
 		shadow_mmu_init_context(vcpu, context, cr0, cr4, efer, new_role);

arch/x86/kvm/svm/nested.c

@@ -380,6 +380,25 @@ static inline bool nested_npt_enabled(struct vcpu_svm *svm)
 	return svm->nested.ctl.nested_ctl & SVM_NESTED_CTL_NP_ENABLE;
 }
 
+static void nested_svm_transition_tlb_flush(struct kvm_vcpu *vcpu)
+{
+	/*
+	 * TODO: optimize unconditional TLB flush/MMU sync.  A partial list of
+	 * things to fix before this can be conditional:
+	 *
+	 *  - Flush TLBs for both L1 and L2 remote TLB flush
+	 *  - Honor L1's request to flush an ASID on nested VMRUN
+	 *  - Sync nested NPT MMU on VMRUN that flushes L2's ASID[*]
+	 *  - Don't crush a pending TLB flush in vmcb02 on nested VMRUN
+	 *  - Flush L1's ASID on KVM_REQ_TLB_FLUSH_GUEST
+	 *
+	 * [*] Unlike nested EPT, SVM's ASID management can invalidate nested
+	 *     NPT guest-physical mappings on VMRUN.
+	 */
+	kvm_make_request(KVM_REQ_MMU_SYNC, vcpu);
+	kvm_make_request(KVM_REQ_TLB_FLUSH_CURRENT, vcpu);
+}
+
 /*
  * Load guest's/host's cr3 on nested vmentry or vmexit. @nested_npt is true
  * if we are emulating VM-Entry into a guest with NPT enabled.
@@ -394,12 +413,8 @@ static int nested_svm_load_cr3(struct kvm_vcpu *vcpu, unsigned long cr3,
 	    CC(!load_pdptrs(vcpu, vcpu->arch.walk_mmu, cr3)))
 		return -EINVAL;
 
-	/*
-	 * TODO: optimize unconditional TLB flush/MMU sync here and in
-	 * kvm_init_shadow_npt_mmu().
-	 */
 	if (!nested_npt)
-		kvm_mmu_new_pgd(vcpu, cr3, false, false);
+		kvm_mmu_new_pgd(vcpu, cr3, true, true);
 
 	vcpu->arch.cr3 = cr3;
 	kvm_register_mark_available(vcpu, VCPU_EXREG_CR3);
@@ -479,6 +494,7 @@ static void nested_vmcb02_prepare_save(struct vcpu_svm *svm, struct vmcb *vmcb12
 static void nested_vmcb02_prepare_control(struct vcpu_svm *svm)
 {
 	const u32 mask = V_INTR_MASKING_MASK | V_GIF_ENABLE_MASK | V_GIF_MASK;
+	struct kvm_vcpu *vcpu = &svm->vcpu;
 
 	/*
 	 * Filled at exit: exit_code, exit_code_hi, exit_info_1, exit_info_2,
@@ -503,10 +519,10 @@ static void nested_vmcb02_prepare_control(struct vcpu_svm *svm)
 
 	/* nested_cr3.  */
 	if (nested_npt_enabled(svm))
-		nested_svm_init_mmu_context(&svm->vcpu);
+		nested_svm_init_mmu_context(vcpu);
 
-	svm->vmcb->control.tsc_offset = svm->vcpu.arch.tsc_offset =
-		svm->vcpu.arch.l1_tsc_offset + svm->nested.ctl.tsc_offset;
+	svm->vmcb->control.tsc_offset = vcpu->arch.tsc_offset =
+		vcpu->arch.l1_tsc_offset + svm->nested.ctl.tsc_offset;
 
 	svm->vmcb->control.int_ctl             =
 		(svm->nested.ctl.int_ctl & ~mask) |
@@ -521,8 +537,10 @@ static void nested_vmcb02_prepare_control(struct vcpu_svm *svm)
 	svm->vmcb->control.pause_filter_count  = svm->nested.ctl.pause_filter_count;
 	svm->vmcb->control.pause_filter_thresh = svm->nested.ctl.pause_filter_thresh;
 
+	nested_svm_transition_tlb_flush(vcpu);
+
 	/* Enter Guest-Mode */
-	enter_guest_mode(&svm->vcpu);
+	enter_guest_mode(vcpu);
 
 	/*
 	 * Merge guest and host intercepts - must be called with vcpu in
@@ -799,6 +817,8 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
 
 	kvm_vcpu_unmap(vcpu, &map, true);
 
+	nested_svm_transition_tlb_flush(vcpu);
+
 	nested_svm_uninit_mmu_context(vcpu);
 
 	rc = nested_svm_load_cr3(vcpu, svm->vmcb->save.cr3, false, true);