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[3/3] KVM: VMX: skip page tracking based on cpuid

Message ID 20210921081010.457591-4-stevensd@google.com (mailing list archive)
State New, archived
Headers show
Series KVM: x86: skip gfn_track allocation when possible | expand

Commit Message

David Stevens Sept. 21, 2021, 8:10 a.m. UTC 
From: David Stevens <stevensd@chromium.org>

Consider X86_FEATURE_VMX when determining whether or not page tracking
is necessary, since that flag can be used to control whether or not a
particular guest supports nested virtualization. When the flag is
toggled, it is necessary to free/allocate gfn_track arrays for any
already existing slots.

If cpuid is heterogeneous or is modified after KVM_RUN, page tracking
may not work properly. This may cause guest instability, as per the
caveat on KVM_SET_CPUID{,2}. Host stability should not be affected.

Signed-off-by: David Stevens <stevensd@chromium.org>
---
 arch/x86/include/asm/kvm_host.h       |  2 +-
 arch/x86/include/asm/kvm_page_track.h |  2 +
 arch/x86/kvm/cpuid.c                  | 55 +++++++++++++++++++++------
 arch/x86/kvm/mmu/page_track.c         | 49 ++++++++++++++++++++++++
 arch/x86/kvm/svm/svm.c                |  4 +-
 arch/x86/kvm/vmx/vmx.c                |  7 +++-
 6 files changed, 104 insertions(+), 15 deletions(-)
diff mbox series

Patch

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index ba29f64d16d3..dc732ac0eb56 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1302,7 +1302,7 @@  struct kvm_x86_ops {
 	void (*hardware_unsetup)(void);
 	bool (*cpu_has_accelerated_tpr)(void);
 	bool (*has_emulated_msr)(struct kvm *kvm, u32 index);
-	void (*vcpu_after_set_cpuid)(struct kvm_vcpu *vcpu);
+	int (*vcpu_after_set_cpuid)(struct kvm_vcpu *vcpu);
 	bool (*nested_enabled)(void);
 
 	unsigned int vm_size;
diff --git a/arch/x86/include/asm/kvm_page_track.h b/arch/x86/include/asm/kvm_page_track.h
index 92e9e2c74219..f917cea1b4b1 100644
--- a/arch/x86/include/asm/kvm_page_track.h
+++ b/arch/x86/include/asm/kvm_page_track.h
@@ -49,6 +49,8 @@  struct kvm_page_track_notifier_node {
 void kvm_page_track_init(struct kvm *kvm, bool mmu_uses_page_tracking);
 void kvm_page_track_cleanup(struct kvm *kvm);
 
+int kvm_page_tracking_mmu_enable(struct kvm *kvm, bool enable);
+
 void kvm_page_track_free_memslot(struct kvm_memory_slot *slot);
 int kvm_page_track_create_memslot(struct kvm *kvm,
 				  struct kvm_memory_slot *slot,
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 739be5da3bca..fb011b0e76e6 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -150,10 +150,11 @@  void kvm_update_cpuid_runtime(struct kvm_vcpu *vcpu)
 }
 EXPORT_SYMBOL_GPL(kvm_update_cpuid_runtime);
 
-static void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
+static int kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 {
 	struct kvm_lapic *apic = vcpu->arch.apic;
 	struct kvm_cpuid_entry2 *best;
+	int ret;
 
 	best = kvm_find_cpuid_entry(vcpu, 1, 0);
 	if (best && apic) {
@@ -198,14 +199,20 @@  static void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 
 	kvm_hv_set_cpuid(vcpu);
 
-	/* Invoke the vendor callback only after the above state is updated. */
-	static_call(kvm_x86_vcpu_after_set_cpuid)(vcpu);
+	/*
+	 * Invoke the vendor callback only after the above state is updated. If
+	 * it fails, continue the function and let the caller roll back to the
+	 * previous cpuid.
+	 */
+	ret = static_call(kvm_x86_vcpu_after_set_cpuid)(vcpu);
 
 	/*
 	 * Except for the MMU, which needs to do its thing any vendor specific
 	 * adjustments to the reserved GPA bits.
 	 */
 	kvm_mmu_after_set_cpuid(vcpu);
+
+	return ret;
 }
 
 static int is_efer_nx(void)
@@ -261,9 +268,9 @@  int kvm_vcpu_ioctl_set_cpuid(struct kvm_vcpu *vcpu,
 			     struct kvm_cpuid *cpuid,
 			     struct kvm_cpuid_entry __user *entries)
 {
-	int r, i;
+	int r, i, orig_nent;
 	struct kvm_cpuid_entry *e = NULL;
-	struct kvm_cpuid_entry2 *e2 = NULL;
+	struct kvm_cpuid_entry2 *e2 = NULL, *orig_e2;
 
 	if (cpuid->nent > KVM_MAX_CPUID_ENTRIES)
 		return -E2BIG;
@@ -298,13 +305,25 @@  int kvm_vcpu_ioctl_set_cpuid(struct kvm_vcpu *vcpu,
 		goto out_free_cpuid;
 	}
 
-	kvfree(vcpu->arch.cpuid_entries);
+	orig_e2 = vcpu->arch.cpuid_entries;
+	orig_nent = vcpu->arch.cpuid_nent;
+
 	vcpu->arch.cpuid_entries = e2;
 	vcpu->arch.cpuid_nent = cpuid->nent;
 
 	cpuid_fix_nx_cap(vcpu);
 	kvm_update_cpuid_runtime(vcpu);
-	kvm_vcpu_after_set_cpuid(vcpu);
+	r = kvm_vcpu_after_set_cpuid(vcpu);
+
+	if (!r) {
+		kvfree(orig_e2);
+	} else {
+		kvfree(e2);
+		vcpu->arch.cpuid_entries = orig_e2;
+		vcpu->arch.cpuid_nent = orig_nent;
+		kvm_update_cpuid_runtime(vcpu);
+		kvm_vcpu_after_set_cpuid(vcpu);
+	}
 
 out_free_cpuid:
 	kvfree(e);
@@ -316,8 +335,8 @@  int kvm_vcpu_ioctl_set_cpuid2(struct kvm_vcpu *vcpu,
 			      struct kvm_cpuid2 *cpuid,
 			      struct kvm_cpuid_entry2 __user *entries)
 {
-	struct kvm_cpuid_entry2 *e2 = NULL;
-	int r;
+	struct kvm_cpuid_entry2 *e2 = NULL, *orig_e2;
+	int r, orig_nent;
 
 	if (cpuid->nent > KVM_MAX_CPUID_ENTRIES)
 		return -E2BIG;
@@ -334,14 +353,26 @@  int kvm_vcpu_ioctl_set_cpuid2(struct kvm_vcpu *vcpu,
 		return r;
 	}
 
-	kvfree(vcpu->arch.cpuid_entries);
+	orig_e2 = vcpu->arch.cpuid_entries;
+	orig_nent = vcpu->arch.cpuid_nent;
+
 	vcpu->arch.cpuid_entries = e2;
 	vcpu->arch.cpuid_nent = cpuid->nent;
 
 	kvm_update_cpuid_runtime(vcpu);
-	kvm_vcpu_after_set_cpuid(vcpu);
+	r = kvm_vcpu_after_set_cpuid(vcpu);
 
-	return 0;
+	if (!r) {
+		kvfree(orig_e2);
+	} else {
+		kvfree(e2);
+		vcpu->arch.cpuid_entries = orig_e2;
+		vcpu->arch.cpuid_nent = orig_nent;
+		kvm_update_cpuid_runtime(vcpu);
+		kvm_vcpu_after_set_cpuid(vcpu);
+	}
+
+	return r;
 }
 
 int kvm_vcpu_ioctl_get_cpuid2(struct kvm_vcpu *vcpu,
diff --git a/arch/x86/kvm/mmu/page_track.c b/arch/x86/kvm/mmu/page_track.c
index c553bc09d50a..e4d0e6ad2178 100644
--- a/arch/x86/kvm/mmu/page_track.c
+++ b/arch/x86/kvm/mmu/page_track.c
@@ -19,6 +19,55 @@ 
 #include "mmu.h"
 #include "mmu_internal.h"
 
+int kvm_page_tracking_mmu_enable(struct kvm *kvm, bool enable)
+{
+	struct kvm_memslots *slots;
+	struct kvm_memory_slot *s;
+	unsigned short **gfn_track, *buf;
+	int i, ret = 0;
+
+	if (IS_ENABLED(CONFIG_KVM_EXTERNAL_WRITE_TRACKING))
+		return 0;
+
+	mutex_lock(&kvm->slots_lock);
+
+	if (enable == kvm->arch.mmu_uses_page_tracking) {
+		mutex_unlock(&kvm->slots_lock);
+		return 0;
+	}
+
+	for (i = 0; enable && i < KVM_ADDRESS_SPACE_NUM && !ret; i++) {
+		slots = __kvm_memslots(kvm, i);
+		kvm_for_each_memslot(s, slots) {
+			gfn_track = s->arch.gfn_track + KVM_PAGE_TRACK_WRITE;
+			*gfn_track = kvcalloc(s->npages, sizeof(*gfn_track),
+					      GFP_KERNEL_ACCOUNT);
+			if (!*gfn_track) {
+				ret = -ENOMEM;
+				break;
+			}
+		}
+	}
+
+	for (i = 0; (!enable || !ret) && i < KVM_ADDRESS_SPACE_NUM; i++) {
+		slots = __kvm_memslots(kvm, i);
+		kvm_for_each_memslot(s, slots) {
+			gfn_track = s->arch.gfn_track + KVM_PAGE_TRACK_WRITE;
+			buf = *gfn_track;
+			*gfn_track = NULL;
+			synchronize_srcu(&kvm->srcu);
+			kvfree(buf);
+		}
+	}
+
+	if (!ret)
+		kvm->arch.mmu_uses_page_tracking = enable;
+
+	mutex_unlock(&kvm->slots_lock);
+
+	return ret;
+}
+
 void kvm_page_track_free_memslot(struct kvm_memory_slot *slot)
 {
 	int i;
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index bcc8f887d3bd..af904e9f4be9 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3981,7 +3981,7 @@  static u64 svm_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio)
 	return 0;
 }
 
-static void svm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
+static int svm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
 	struct kvm_cpuid_entry2 *best;
@@ -4047,6 +4047,8 @@  static void svm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 		set_msr_interception(vcpu, svm->msrpm, MSR_IA32_SYSENTER_EIP, 1, 1);
 		set_msr_interception(vcpu, svm->msrpm, MSR_IA32_SYSENTER_ESP, 1, 1);
 	}
+
+	return 0;
 }
 
 static bool svm_nested_enabled(void)
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 1b21ed01e837..6455759907d1 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7166,7 +7166,7 @@  static void update_intel_pt_cfg(struct kvm_vcpu *vcpu)
 		vmx->pt_desc.ctl_bitmask &= ~(0xfULL << (32 + i * 4));
 }
 
-static void vmx_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
+static int vmx_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 
@@ -7223,6 +7223,11 @@  static void vmx_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 
 	/* Refresh #PF interception to account for MAXPHYADDR changes. */
 	vmx_update_exception_bitmap(vcpu);
+
+	if (tdp_enabled)
+		return kvm_page_tracking_mmu_enable(vcpu->kvm,
+						    nested_vmx_allowed(vcpu));
+	return 0;
 }
 
 static bool vmx_nested_enabled(void)