[PATCH 21/26] KVM: x86: asi: Restricted address space for VM execution

[Brendan Jackman]

An ASI restricted address space is added for KVM. It is currently only
enabled for Intel CPUs.

This change incorporates an extra asi_exit at the end of vcpu_run. We
expect later iterations of ASI to drop that call as we gain the
ablity to context switch within the ASI domain.

Signed-off-by: Brendan Jackman <jackmanb@xxxxxxxxxx>
---
 arch/x86/include/asm/kvm_host.h |  3 +++
 arch/x86/kvm/svm/svm.c          |  2 ++
 arch/x86/kvm/vmx/vmx.c          | 36 ++++++++++++++++++++++--------------
 arch/x86/kvm/x86.c              | 29 +++++++++++++++++++++++++++--
 4 files changed, 54 insertions(+), 16 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 6efd1497b0263..6c3326cb8273c 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -36,6 +36,7 @@
 #include <asm/kvm_page_track.h>
 #include <asm/kvm_vcpu_regs.h>
 #include <asm/hyperv-tlfs.h>
+#include <asm/asi.h>
 
 #define __KVM_HAVE_ARCH_VCPU_DEBUGFS
 
@@ -1514,6 +1515,8 @@ struct kvm_arch {
 	 */
 #define SPLIT_DESC_CACHE_MIN_NR_OBJECTS (SPTE_ENT_PER_PAGE + 1)
 	struct kvm_mmu_memory_cache split_desc_cache;
+
+	struct asi *asi;
 };
 
 struct kvm_vm_stat {
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 9aaf83c8d57df..6f9a279c12dc7 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4108,6 +4108,7 @@ static noinstr void svm_vcpu_enter_exit(struct kvm_vcpu *vcpu, bool spec_ctrl_in
 	guest_state_enter_irqoff();
 
 	amd_clear_divider();
+	asi_enter(vcpu->kvm->arch.asi);
 
 	if (sev_es_guest(vcpu->kvm))
 		__svm_sev_es_vcpu_run(svm, spec_ctrl_intercepted,
@@ -4115,6 +4116,7 @@ static noinstr void svm_vcpu_enter_exit(struct kvm_vcpu *vcpu, bool spec_ctrl_in
 	else
 		__svm_vcpu_run(svm, spec_ctrl_intercepted);
 
+	asi_relax();
 	guest_state_exit_irqoff();
 }
 
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 22411f4aff530..1105d666a8ade 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -49,6 +49,7 @@
 #include <asm/mwait.h>
 #include <asm/spec-ctrl.h>
 #include <asm/vmx.h>
+#include <asm/asi.h>
 
 #include <trace/events/ipi.h>
 
@@ -7255,14 +7256,32 @@ static noinstr void vmx_vcpu_enter_exit(struct kvm_vcpu *vcpu,
 					unsigned int flags)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
+	unsigned long cr3;
 
 	guest_state_enter_irqoff();
+	asi_enter(vcpu->kvm->arch.asi);
+
+	/*
+	 * Refresh vmcs.HOST_CR3 if necessary.  This must be done immediately
+	 * prior to VM-Enter, as the kernel may load a new ASID (PCID) any time
+	 * it switches back to the current->mm, which can occur in KVM context
+	 * when switching to a temporary mm to patch kernel code, e.g. if KVM
+	 * toggles a static key while handling a VM-Exit.
+	 * Also, this must be done after asi_enter(), as it changes CR3
+	 * when switching address spaces.
+	 */
+	cr3 = __get_current_cr3_fast();
+	if (unlikely(cr3 != vmx->loaded_vmcs->host_state.cr3)) {
+		vmcs_writel(HOST_CR3, cr3);
+		vmx->loaded_vmcs->host_state.cr3 = cr3;
+	}
 
 	/*
 	 * L1D Flush includes CPU buffer clear to mitigate MDS, but VERW
 	 * mitigation for MDS is done late in VMentry and is still
 	 * executed in spite of L1D Flush. This is because an extra VERW
 	 * should not matter much after the big hammer L1D Flush.
+	 * This is only after asi_enter() for performance reasons.
 	 */
 	if (static_branch_unlikely(&vmx_l1d_should_flush))
 		vmx_l1d_flush(vcpu);
@@ -7283,6 +7302,8 @@ static noinstr void vmx_vcpu_enter_exit(struct kvm_vcpu *vcpu,
 
 	vmx->idt_vectoring_info = 0;
 
+	asi_relax();
+
 	vmx_enable_fb_clear(vmx);
 
 	if (unlikely(vmx->fail)) {
@@ -7311,7 +7332,7 @@ static noinstr void vmx_vcpu_enter_exit(struct kvm_vcpu *vcpu,
 static fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu, bool force_immediate_exit)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
-	unsigned long cr3, cr4;
+	unsigned long cr4;
 
 	/* Record the guest's net vcpu time for enforced NMI injections. */
 	if (unlikely(!enable_vnmi &&
@@ -7354,19 +7375,6 @@ static fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu, bool force_immediate_exit)
 		vmcs_writel(GUEST_RIP, vcpu->arch.regs[VCPU_REGS_RIP]);
 	vcpu->arch.regs_dirty = 0;
 
-	/*
-	 * Refresh vmcs.HOST_CR3 if necessary.  This must be done immediately
-	 * prior to VM-Enter, as the kernel may load a new ASID (PCID) any time
-	 * it switches back to the current->mm, which can occur in KVM context
-	 * when switching to a temporary mm to patch kernel code, e.g. if KVM
-	 * toggles a static key while handling a VM-Exit.
-	 */
-	cr3 = __get_current_cr3_fast();
-	if (unlikely(cr3 != vmx->loaded_vmcs->host_state.cr3)) {
-		vmcs_writel(HOST_CR3, cr3);
-		vmx->loaded_vmcs->host_state.cr3 = cr3;
-	}
-
 	cr4 = cr4_read_shadow();
 	if (unlikely(cr4 != vmx->loaded_vmcs->host_state.cr4)) {
 		vmcs_writel(HOST_CR4, cr4);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 91478b769af08..b9947e88d4ac6 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -85,6 +85,7 @@
 #include <asm/emulate_prefix.h>
 #include <asm/sgx.h>
 #include <clocksource/hyperv_timer.h>
+#include <asm/asi.h>
 
 #define CREATE_TRACE_POINTS
 #include "trace.h"
@@ -318,6 +319,8 @@ u64 __read_mostly host_xcr0;
 
 static struct kmem_cache *x86_emulator_cache;
 
+static int __read_mostly kvm_asi_index = -1;
+
 /*
  * When called, it means the previous get/set msr reached an invalid msr.
  * Return true if we want to ignore/silent this failed msr access.
@@ -9750,6 +9753,11 @@ int kvm_x86_vendor_init(struct kvm_x86_init_ops *ops)
 	if (r)
 		goto out_free_percpu;
 
+	r = asi_register_class("KVM", NULL);
+	if (r < 0)
+		goto out_mmu_exit;
+	kvm_asi_index = r;
+
 	if (boot_cpu_has(X86_FEATURE_XSAVE)) {
 		host_xcr0 = xgetbv(XCR_XFEATURE_ENABLED_MASK);
 		kvm_caps.supported_xcr0 = host_xcr0 & KVM_SUPPORTED_XCR0;
@@ -9767,7 +9775,7 @@ int kvm_x86_vendor_init(struct kvm_x86_init_ops *ops)
 
 	r = ops->hardware_setup();
 	if (r != 0)
-		goto out_mmu_exit;
+		goto out_asi_unregister;
 
 	kvm_ops_update(ops);
 
@@ -9820,6 +9828,8 @@ int kvm_x86_vendor_init(struct kvm_x86_init_ops *ops)
 out_unwind_ops:
 	kvm_x86_ops.hardware_enable = NULL;
 	static_call(kvm_x86_hardware_unsetup)();
+out_asi_unregister:
+	asi_unregister_class(kvm_asi_index);
 out_mmu_exit:
 	kvm_mmu_vendor_module_exit();
 out_free_percpu:
@@ -9851,6 +9861,7 @@ void kvm_x86_vendor_exit(void)
 	cancel_work_sync(&pvclock_gtod_work);
 #endif
 	static_call(kvm_x86_hardware_unsetup)();
+	asi_unregister_class(kvm_asi_index);
 	kvm_mmu_vendor_module_exit();
 	free_percpu(user_return_msrs);
 	kmem_cache_destroy(x86_emulator_cache);
@@ -11436,6 +11447,13 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
 
 	r = vcpu_run(vcpu);
 
+	/*
+	 * At present ASI doesn't have the capability to transition directly
+	 * from the restricted address space to the user address space. So we
+	 * just return to the unrestricted address space in between.
+	 */
+	asi_exit();
+
 out:
 	kvm_put_guest_fpu(vcpu);
 	if (kvm_run->kvm_valid_regs)
@@ -12539,10 +12557,14 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
 
 	kvm_mmu_init_vm(kvm);
 
-	ret = static_call(kvm_x86_vm_init)(kvm);
+	ret = asi_init(kvm->mm, kvm_asi_index, &kvm->arch.asi);
 	if (ret)
 		goto out_uninit_mmu;
 
+	ret = static_call(kvm_x86_vm_init)(kvm);
+	if (ret)
+		goto out_asi_destroy;
+
 	INIT_HLIST_HEAD(&kvm->arch.mask_notifier_list);
 	atomic_set(&kvm->arch.noncoherent_dma_count, 0);
 
@@ -12579,6 +12601,8 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
 
 	return 0;
 
+out_asi_destroy:
+	asi_destroy(kvm->arch.asi);
 out_uninit_mmu:
 	kvm_mmu_uninit_vm(kvm);
 	kvm_page_track_cleanup(kvm);
@@ -12720,6 +12744,7 @@ void kvm_arch_destroy_vm(struct kvm *kvm)
 	kvm_destroy_vcpus(kvm);
 	kvfree(rcu_dereference_check(kvm->arch.apic_map, 1));
 	kfree(srcu_dereference_check(kvm->arch.pmu_event_filter, &kvm->srcu, 1));
+	asi_destroy(kvm->arch.asi);
 	kvm_mmu_uninit_vm(kvm);
 	kvm_page_track_cleanup(kvm);
 	kvm_xen_destroy_vm(kvm);

-- 
2.45.2.993.g49e7a77208-goog