[RFC PATCH 4/4] KVM: TDX: Check KVM exit on KVM_HC_MAP_GPA_RANGE when TD finalize

[Binbin Wu <binbin.wu@linux.intel.com>]

Check userspace has enabled KVM exit on KVM_HC_MAP_GPA_RANGE during
KVM_TDX_FINALIZE_VM.

TDVMCALL_MAP_GPA is one of the GHCI base TDVMCALLs, so it must be
implemented by VMM to support TDX guests. KVM converts TDVMCALL_MAP_GPA
to KVM_HC_MAP_GPA_RANGE, which requires userspace to enable
KVM_CAP_EXIT_HYPERCALL with KVM_HC_MAP_GPA_RANGE bit set. Check it when
userspace requests KVM_TDX_FINALIZE_VM, so that there is no need to check
it during TDX guests running.

Signed-off-by: Binbin Wu <binbin.wu@linux.intel.com>
---
 Documentation/virt/kvm/x86/intel-tdx.rst |  3 +++
 arch/x86/kvm/vmx/tdx.c                   | 20 +++++++++-----------
 2 files changed, 12 insertions(+), 11 deletions(-)

diff --git a/Documentation/virt/kvm/x86/intel-tdx.rst b/Documentation/virt/kvm/x86/intel-tdx.rst
index 69c64453e9ca..41e38c38b034 100644
--- a/Documentation/virt/kvm/x86/intel-tdx.rst
+++ b/Documentation/virt/kvm/x86/intel-tdx.rst
@@ -246,6 +246,9 @@ control flow is as follows:
    * Prepare content of initial guest memory.
    * KVM_TDX_INIT_MEM_REGION: Add initial guest memory.
    * KVM_TDX_FINALIZE_VM: Finalize the measurement of the TDX guest.
+     Note: To support TDVMCALL_MAP_GPA, userspace must opt-in
+     KVM_CAP_EXIT_HYPERCALL with KVM_HC_MAP_GPA_RANGE before calling
+     KVM_TDX_FINALIZE_VM.
 
 #. Run VCPU
 
diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index a3cd68f44a9c..7fc6e6b9c131 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -1209,17 +1209,6 @@ static int tdx_map_gpa(struct kvm_vcpu *vcpu)
 	u64 size = tdx->vp_enter_args.r13;
 	u64 ret;
 
-	/*
-	 * Converting TDVMCALL_MAP_GPA to KVM_HC_MAP_GPA_RANGE requires
-	 * userspace to enable KVM_CAP_EXIT_HYPERCALL with KVM_HC_MAP_GPA_RANGE
-	 * bit set.  If not, the error code is not defined in GHCI for TDX, use
-	 * TDVMCALL_STATUS_INVALID_OPERAND for this case.
-	 */
-	if (!user_exit_on_hypercall(vcpu->kvm, KVM_HC_MAP_GPA_RANGE)) {
-		ret = TDVMCALL_STATUS_INVALID_OPERAND;
-		goto error;
-	}
-
 	if (gpa + size <= gpa || !kvm_vcpu_is_legal_gpa(vcpu, gpa) ||
 	    !kvm_vcpu_is_legal_gpa(vcpu, gpa + size - 1) ||
 	    (vt_is_tdx_private_gpa(vcpu->kvm, gpa) !=
@@ -2821,6 +2810,15 @@ static int tdx_td_finalize(struct kvm *kvm, struct kvm_tdx_cmd *cmd)
 {
 	struct kvm_tdx *kvm_tdx = to_kvm_tdx(kvm);
 
+	/*
+	 * TDVMCALL_MAP_GPA is one of the GHCI base TDVMCALLs, so it must be
+	 * implemented by VMM to support TDX guests. KVM converts
+	 * TDVMCALL_MAP_GPA to KVM_HC_MAP_GPA_RANGE, which requires userspace to
+	 * enable KVM_CAP_EXIT_HYPERCALL with KVM_HC_MAP_GPA_RANGE bit set.
+	 */
+	if (!user_exit_on_hypercall(kvm, KVM_HC_MAP_GPA_RANGE))
+		return -EINVAL;
+
 	guard(mutex)(&kvm->slots_lock);
 
 	if (!is_hkid_assigned(kvm_tdx) || kvm_tdx->state == TD_STATE_RUNNABLE)
-- 
2.46.0