KVM: nVMX: Add support for capturing highest observable L2 TSC

The L1 hypervisor may include the IA32_TIME_STAMP_COUNTER MSR in the
vmcs12 MSR VM-exit MSR-store area as a way of determining the highest
TSC value that might have been observed by L2 prior to VM-exit. The
current implementation does not capture a very tight bound on this
value.  To tighten the bound, add the IA32_TIME_STAMP_COUNTER MSR to the
vmcs02 VM-exit MSR-store area whenever it appears in the vmcs12 VM-exit
MSR-store area.  When L0 processes the vmcs12 VM-exit MSR-store area
during the emulation of an L2->L1 VM-exit, special-case the
IA32_TIME_STAMP_COUNTER MSR, using the value stored in the vmcs02
VM-exit MSR-store area to derive the value to be stored in the vmcs12
VM-exit MSR-store area.

Reviewed-by: Liran Alon <liran.alon@oracle.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Aaron Lewis <aaronlewis@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

3 files changed, 101 insertions, 7 deletions

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 3ef529cc72fb88..60d42ce424034e 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -940,6 +940,37 @@ fail:
 	return i + 1;
 }
 
+static bool nested_vmx_get_vmexit_msr_value(struct kvm_vcpu *vcpu,
+					    u32 msr_index,
+					    u64 *data)
+{
+	struct vcpu_vmx *vmx = to_vmx(vcpu);
+
+	/*
+	 * If the L0 hypervisor stored a more accurate value for the TSC that
+	 * does not include the time taken for emulation of the L2->L1
+	 * VM-exit in L0, use the more accurate value.
+	 */
+	if (msr_index == MSR_IA32_TSC) {
+		int index = vmx_find_msr_index(&vmx->msr_autostore.guest,
+					       MSR_IA32_TSC);
+
+		if (index >= 0) {
+			u64 val = vmx->msr_autostore.guest.val[index].value;
+
+			*data = kvm_read_l1_tsc(vcpu, val);
+			return true;
+		}
+	}
+
+	if (kvm_get_msr(vcpu, msr_index, data)) {
+		pr_debug_ratelimited("%s cannot read MSR (0x%x)\n", __func__,
+			msr_index);
+		return false;
+	}
+	return true;
+}
+
 static bool read_and_check_msr_entry(struct kvm_vcpu *vcpu, u64 gpa, int i,
 				     struct vmx_msr_entry *e)
 {
@@ -974,12 +1005,9 @@ static int nested_vmx_store_msr(struct kvm_vcpu *vcpu, u64 gpa, u32 count)
 		if (!read_and_check_msr_entry(vcpu, gpa, i, &e))
 			return -EINVAL;
 
-		if (kvm_get_msr(vcpu, e.index, &data)) {
-			pr_debug_ratelimited(
-				"%s cannot read MSR (%u, 0x%x)\n",
-				__func__, i, e.index);
+		if (!nested_vmx_get_vmexit_msr_value(vcpu, e.index, &data))
 			return -EINVAL;
-		}
+
 		if (kvm_vcpu_write_guest(vcpu,
 					 gpa + i * sizeof(e) +
 					     offsetof(struct vmx_msr_entry, value),
@@ -993,6 +1021,60 @@ static int nested_vmx_store_msr(struct kvm_vcpu *vcpu, u64 gpa, u32 count)
 	return 0;
 }
 
+static bool nested_msr_store_list_has_msr(struct kvm_vcpu *vcpu, u32 msr_index)
+{
+	struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
+	u32 count = vmcs12->vm_exit_msr_store_count;
+	u64 gpa = vmcs12->vm_exit_msr_store_addr;
+	struct vmx_msr_entry e;
+	u32 i;
+
+	for (i = 0; i < count; i++) {
+		if (!read_and_check_msr_entry(vcpu, gpa, i, &e))
+			return false;
+
+		if (e.index == msr_index)
+			return true;
+	}
+	return false;
+}
+
+static void prepare_vmx_msr_autostore_list(struct kvm_vcpu *vcpu,
+					   u32 msr_index)
+{
+	struct vcpu_vmx *vmx = to_vmx(vcpu);
+	struct vmx_msrs *autostore = &vmx->msr_autostore.guest;
+	bool in_vmcs12_store_list;
+	int msr_autostore_index;
+	bool in_autostore_list;
+	int last;
+
+	msr_autostore_index = vmx_find_msr_index(autostore, msr_index);
+	in_autostore_list = msr_autostore_index >= 0;
+	in_vmcs12_store_list = nested_msr_store_list_has_msr(vcpu, msr_index);
+
+	if (in_vmcs12_store_list && !in_autostore_list) {
+		if (autostore->nr == NR_LOADSTORE_MSRS) {
+			/*
+			 * Emulated VMEntry does not fail here.  Instead a less
+			 * accurate value will be returned by
+			 * nested_vmx_get_vmexit_msr_value() using kvm_get_msr()
+			 * instead of reading the value from the vmcs02 VMExit
+			 * MSR-store area.
+			 */
+			pr_warn_ratelimited(
+				"Not enough msr entries in msr_autostore.  Can't add msr %x\n",
+				msr_index);
+			return;
+		}
+		last = autostore->nr++;
+		autostore->val[last].index = msr_index;
+	} else if (!in_vmcs12_store_list && in_autostore_list) {
+		last = --autostore->nr;
+		autostore->val[msr_autostore_index] = autostore->val[last];
+	}
+}
+
 static bool nested_cr3_valid(struct kvm_vcpu *vcpu, unsigned long val)
 {
 	unsigned long invalid_mask;
@@ -2038,7 +2120,7 @@ static void prepare_vmcs02_constant_state(struct vcpu_vmx *vmx)
 	 * addresses are constant (for vmcs02), the counts can change based
 	 * on L2's behavior, e.g. switching to/from long mode.
 	 */
-	vmcs_write32(VM_EXIT_MSR_STORE_COUNT, 0);
+	vmcs_write64(VM_EXIT_MSR_STORE_ADDR, __pa(vmx->msr_autostore.guest.val));
 	vmcs_write64(VM_EXIT_MSR_LOAD_ADDR, __pa(vmx->msr_autoload.host.val));
 	vmcs_write64(VM_ENTRY_MSR_LOAD_ADDR, __pa(vmx->msr_autoload.guest.val));
 
@@ -2306,6 +2388,13 @@ static void prepare_vmcs02_rare(struct vcpu_vmx *vmx, struct vmcs12 *vmcs12)
 		vmcs_write64(EOI_EXIT_BITMAP3, vmcs12->eoi_exit_bitmap3);
 	}
 
+	/*
+	 * Make sure the msr_autostore list is up to date before we set the
+	 * count in the vmcs02.
+	 */
+	prepare_vmx_msr_autostore_list(&vmx->vcpu, MSR_IA32_TSC);
+
+	vmcs_write32(VM_EXIT_MSR_STORE_COUNT, vmx->msr_autostore.guest.nr);
 	vmcs_write32(VM_EXIT_MSR_LOAD_COUNT, vmx->msr_autoload.host.nr);
 	vmcs_write32(VM_ENTRY_MSR_LOAD_COUNT, vmx->msr_autoload.guest.nr);
 
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 7b191963dde14c..621142e55e2873 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -833,7 +833,7 @@ static void clear_atomic_switch_msr_special(struct vcpu_vmx *vmx,
 	vm_exit_controls_clearbit(vmx, exit);
 }
 
-static int vmx_find_msr_index(struct vmx_msrs *m, u32 msr)
+int vmx_find_msr_index(struct vmx_msrs *m, u32 msr)
 {
 	unsigned int i;
 
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index 73ff03091d294f..90b97d9d4f7d2d 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -233,6 +233,10 @@ struct vcpu_vmx {
 		struct vmx_msrs host;
 	} msr_autoload;
 
+	struct msr_autostore {
+		struct vmx_msrs guest;
+	} msr_autostore;
+
 	struct {
 		int vm86_active;
 		ulong save_rflags;
@@ -337,6 +341,7 @@ void vmx_set_virtual_apic_mode(struct kvm_vcpu *vcpu);
 struct shared_msr_entry *find_msr_entry(struct vcpu_vmx *vmx, u32 msr);
 void pt_update_intercept_for_msr(struct vcpu_vmx *vmx);
 void vmx_update_host_rsp(struct vcpu_vmx *vmx, unsigned long host_rsp);
+int vmx_find_msr_index(struct vmx_msrs *m, u32 msr);
 
 #define POSTED_INTR_ON  0
 #define POSTED_INTR_SN  1