linux-kernel - [PATCH 1/7] KVM: nVMX: Introduce nested_evmcs_is

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Date:   Tue, 11 May 2021 13:19:50 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Maxim Levitsky <mlevitsk@...hat.com>
Subject: [PATCH 1/7] KVM: nVMX: Introduce nested_evmcs_is_used()

Unlike regular set_current_vmptr(), nested_vmx_handle_enlightened_vmptrld()
can not be called directly from vmx_set_nested_state() as KVM may not have
all the information yet (e.g. HV_X64_MSR_VP_ASSIST_PAGE MSR may not be
restored yet). Enlightened VMCS is mapped later while getting nested state
pages. In the meantime, vmx->nested.hv_evmcs remains NULL and using it
for various checks is incorrect. In particular, if KVM_GET_NESTED_STATE is
called right after KVM_SET_NESTED_STATE, KVM_STATE_NESTED_EVMCS flag in the
resulting state will be unset (and such state will later fail to load).

Introduce nested_evmcs_is_used() and use 'is_guest_mode(vcpu) &&
vmx->nested.current_vmptr == -1ull' check to detect not-yet-mapped eVMCS
after restore.

Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
---
 arch/x86/kvm/vmx/nested.c | 31 ++++++++++++++++++++++++++-----
 1 file changed, 26 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 6058a65a6ede..3080e00c8f90 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -141,6 +141,27 @@ static void init_vmcs_shadow_fields(void)
 	max_shadow_read_write_fields = j;
 }
 
+static inline bool nested_evmcs_is_used(struct vcpu_vmx *vmx)
+{
+	struct kvm_vcpu *vcpu = &vmx->vcpu;
+
+	if (vmx->nested.hv_evmcs)
+		return true;
+
+	/*
+	 * After KVM_SET_NESTED_STATE, enlightened VMCS is mapped during
+	 * KVM_REQ_GET_NESTED_STATE_PAGES handling and until the request is
+	 * processed vmx->nested.hv_evmcs is NULL. It is, however, possible to
+	 * detect such state by checking 'nested.current_vmptr == -1ull' when
+	 * vCPU is in guest mode, it is only possible with eVMCS.
+	 */
+	if (unlikely(vmx->nested.enlightened_vmcs_enabled && is_guest_mode(vcpu) &&
+		     (vmx->nested.current_vmptr == -1ull)))
+		return true;
+
+	return false;
+}
+
 /*
  * The following 3 functions, nested_vmx_succeed()/failValid()/failInvalid(),
  * set the success or error code of an emulated VMX instruction (as specified
@@ -187,7 +208,7 @@ static int nested_vmx_fail(struct kvm_vcpu *vcpu, u32 vm_instruction_error)
 	 * failValid writes the error number to the current VMCS, which
 	 * can't be done if there isn't a current VMCS.
 	 */
-	if (vmx->nested.current_vmptr == -1ull && !vmx->nested.hv_evmcs)
+	if (vmx->nested.current_vmptr == -1ull && !nested_evmcs_is_used(vmx))
 		return nested_vmx_failInvalid(vcpu);
 
 	return nested_vmx_failValid(vcpu, vm_instruction_error);
@@ -2208,7 +2229,7 @@ static void prepare_vmcs02_early(struct vcpu_vmx *vmx, struct vmcs12 *vmcs12)
 	u32 exec_control;
 	u64 guest_efer = nested_vmx_calc_efer(vmx, vmcs12);
 
-	if (vmx->nested.dirty_vmcs12 || vmx->nested.hv_evmcs)
+	if (vmx->nested.dirty_vmcs12 || nested_evmcs_is_used(vmx))
 		prepare_vmcs02_early_rare(vmx, vmcs12);
 
 	/*
@@ -3437,7 +3458,7 @@ enum nvmx_vmentry_status nested_vmx_enter_non_root_mode(struct kvm_vcpu *vcpu,
 
 	load_vmcs12_host_state(vcpu, vmcs12);
 	vmcs12->vm_exit_reason = exit_reason.full;
-	if (enable_shadow_vmcs || vmx->nested.hv_evmcs)
+	if (enable_shadow_vmcs || nested_evmcs_is_used(vmx))
 		vmx->nested.need_vmcs12_to_shadow_sync = true;
 	return NVMX_VMENTRY_VMEXIT;
 }
@@ -4032,7 +4053,7 @@ static void sync_vmcs02_to_vmcs12(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 
-	if (vmx->nested.hv_evmcs)
+	if (nested_evmcs_is_used(vmx))
 		sync_vmcs02_to_vmcs12_rare(vcpu, vmcs12);
 
 	vmx->nested.need_sync_vmcs02_to_vmcs12_rare = !vmx->nested.hv_evmcs;
@@ -6056,7 +6077,7 @@ static int vmx_get_nested_state(struct kvm_vcpu *vcpu,
 		if (vmx_has_valid_vmcs12(vcpu)) {
 			kvm_state.size += sizeof(user_vmx_nested_state->vmcs12);
 
-			if (vmx->nested.hv_evmcs)
+			if (nested_evmcs_is_used(vmx))
 				kvm_state.flags |= KVM_STATE_NESTED_EVMCS;
 
 			if (is_guest_mode(vcpu) &&
-- 
2.30.2