[RFC PATCH 13/15] KVM: TDX: Support event-notify interrupts only with userspace quoting

[Xu Yilun]

From: Peter Fang <peter.fang@xxxxxxxxx>

Tie userspace SetupEventNotifyInterrupt support to userspace Quote
generation. Delivering event-notify interrupts via userspace breaks if
KVM never exits to userspace in the first place.

No known guest currently requires event-notify interrupt support, so
defer adding in-kernel support for now. Linux TDX guests use polling
only.

Update the KVM API Documentation to reflect the change.

Signed-off-by: Peter Fang <peter.fang@xxxxxxxxx>
Signed-off-by: Xu Yilun <yilun.xu@xxxxxxxxxxxxxxx>
---
 Documentation/virt/kvm/api.rst |  8 +++++++-
 arch/x86/kvm/vmx/tdx.c         | 20 +++++++++++++++++---
 2 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 52bbbb553ce1..8a02745a36ee 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -7335,6 +7335,9 @@ inputs and outputs of the TDVMCALL.  Currently the following values of
    queued successfully, the TDX guest can poll the status field in the
    shared-memory area to check whether the Quote generation is completed or
    not. When completed, the generated Quote is returned via the same buffer.
+   If the host kernel generates Quotes through the TDX Quoting service provided
+   by the TDX module, KVM processes the GetQuote request and it will not appear
+   in userspace.  KVM only supports version 1 of the GetQuote request.
 
  * ``TDVMCALL_GET_TD_VM_CALL_INFO``: the guest has requested the support
    status of TDVMCALLs.  The output values for the given leaf should be
@@ -7342,7 +7345,10 @@ inputs and outputs of the TDVMCALL.  Currently the following values of
    field of the union.
 
  * ``TDVMCALL_SETUP_EVENT_NOTIFY_INTERRUPT``: the guest has requested to
-   set up a notification interrupt for vector ``vector``.
+   set up a notification interrupt for vector ``vector``.  Since this TDVMCALL
+   is used to optimize ``TDVMCALL_GET_QUOTE``, KVM disables this support in
+   userspace VMM if ``TDVMCALL_GET_QUOTE`` is completely handled in the kernel.
+   KVM may add kernel support for this in the future.
 
 KVM may add support for more values in the future that may cause a userspace
 exit, even without calls to ``KVM_ENABLE_CAP`` or similar.  In this case,
diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index bade046da5a1..5aebbec7fa6e 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -185,7 +185,7 @@ static void td_init_cpuid_entry2(struct kvm_cpuid_entry2 *entry, unsigned char i
 	tdx_clear_unsupported_cpuid(entry);
 }
 
-#define TDVMCALLINFO_SETUP_EVENT_NOTIFY_INTERRUPT	BIT(1)
+#define TDVMCALLINFO_SETUP_EVENT_NOTIFY_INTERRUPT	BIT_ULL(1)
 
 static int init_kvm_tdx_caps(const struct tdx_sys_info_td_conf *td_conf,
 			     struct kvm_tdx_capabilities *caps)
@@ -202,8 +202,15 @@ static int init_kvm_tdx_caps(const struct tdx_sys_info_td_conf *td_conf,
 
 	caps->cpuid.nent = td_conf->num_cpuid_config;
 
-	caps->user_tdvmcallinfo_1_r11 =
-		TDVMCALLINFO_SETUP_EVENT_NOTIFY_INTERRUPT;
+	/*
+	 * Don't advertise userspace event-notify interrupt support if TDX
+	 * quoting service is enabled, as quote generation will be done entirely
+	 * in the kernel. Support in the kernel can be added later if needed.
+	 */
+	if (!tdx_quote_enabled()) {
+		caps->user_tdvmcallinfo_1_r11 |=
+			TDVMCALLINFO_SETUP_EVENT_NOTIFY_INTERRUPT;
+	}
 
 	for (i = 0; i < td_conf->num_cpuid_config; i++)
 		td_init_cpuid_entry2(&caps->cpuid.entries[i], i);
@@ -1684,9 +1691,16 @@ static int tdx_get_quote(struct kvm_vcpu *vcpu)
 
 static int tdx_setup_event_notify_interrupt(struct kvm_vcpu *vcpu)
 {
+	struct kvm_tdx *kvm_tdx = to_kvm_tdx(vcpu->kvm);
 	struct vcpu_tdx *tdx = to_tdx(vcpu);
 	u64 vector = tdx->vp_enter_args.r12;
 
+	/* See init_kvm_tdx_caps() for comments */
+	if (kvm_tdx->get_quote_in_kernel) {
+		tdvmcall_set_return_code(vcpu, TDVMCALL_STATUS_SUBFUNC_UNSUPPORTED);
+		return 1;
+	}
+
 	if (vector < 32 || vector > 255) {
 		tdvmcall_set_return_code(vcpu, TDVMCALL_STATUS_INVALID_OPERAND);
 		return 1;
-- 
2.25.1