[PATCH 6.18.y] KVM: TDX: Don't assume exit_reason[31:16] is all-0 in tdx_to_vmx_exit_reason()

[Sasha Levin <sashal@kernel.org>]

From: Xiaoyao Li <xiaoyao.li@intel.com>

[ Upstream commit bc335ce04408750585b4b32f248c543c9493d545 ]

When handling the real Exit Reason, don't assume the upper 16 bits as
all-0 in tdx_to_vmx_exit_reason(), in preparation for enabling Bus Lock
VM exit.

When Bus Lock VM exit is enabled, the bit 26 of Exit Reason becomes
valid and it can be 1 with various exit reasons.  Change the logic in
tdx_to_vmx_exit_reason() to check the 'basic' Exit Reason for correctness.
Also preserve bit[31:16] when changing the (basic) Exit Reason, to not
lose the information in bit[31:16].

Change the return type of tdx_to_vmx_exit_reason() to
"union vmx_exit_reason" for the convenience of manipulating the basic
field.

Fixes: c42856af8f70 ("KVM: TDX: Add a place holder for handler of TDX hypercalls (TDG.VP.VMCALL)")
Cc: stable@vger.kernel.org
Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
Link: https://patch.msgid.link/20260819094903.3060020-5-xiaoyao.li@intel.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
Depends on <20261106144334.354667-1-sashal@kernel.org>

 arch/x86/kvm/vmx/tdx.c | 24 ++++++++++++++----------
 1 file changed, 14 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index ad5b5497473a5..2739e60bd06a2 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -899,10 +899,10 @@ static __always_inline bool tdx_is_exit_reason_valid(u64 vp_enter_ret)
 	}
 }
 
-static __always_inline u32 tdx_to_vmx_exit_reason(struct kvm_vcpu *vcpu)
+static __always_inline union vmx_exit_reason tdx_to_vmx_exit_reason(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_tdx *tdx = to_tdx(vcpu);
-	u32 exit_reason;
+	union vmx_exit_reason exit_reason;
 
 	/*
 	 * Return the synthesized invalid Exit Reason, as the TDX module
@@ -910,22 +910,26 @@ static __always_inline u32 tdx_to_vmx_exit_reason(struct kvm_vcpu *vcpu)
 	 * but this is NOT a failed VM-Enter.
 	 */
 	if (!tdx_is_exit_reason_valid(tdx->vp_enter_ret))
-		return EXIT_REASON_UNDEFINED;
+		return (union vmx_exit_reason) {
+			.basic = EXIT_REASON_UNDEFINED,
+		};
 
-	exit_reason = tdx->vp_enter_ret;
+	exit_reason.full = (u32)tdx->vp_enter_ret;
 
-	switch (exit_reason) {
+	switch (exit_reason.basic) {
 	case EXIT_REASON_TDCALL:
 		if (tdvmcall_exit_type(vcpu))
-			return EXIT_REASON_VMCALL;
-
-		return tdcall_to_vmx_exit_reason(vcpu);
+			exit_reason.basic = EXIT_REASON_VMCALL;
+		else
+			exit_reason.basic = tdcall_to_vmx_exit_reason(vcpu);
+		break;
 	case EXIT_REASON_EPT_MISCONFIG:
 		/*
 		 * Defer KVM_BUG_ON() until tdx_handle_exit() because this is in
 		 * non-instrumentable code with interrupts disabled.
 		 */
-		return EXIT_REASON_UNDEFINED;
+		exit_reason.basic = EXIT_REASON_UNDEFINED;
+		break;
 	default:
 		break;
 	}
@@ -942,7 +946,7 @@ static noinstr void tdx_vcpu_enter_exit(struct kvm_vcpu *vcpu)
 
 	tdx->vp_enter_ret = tdh_vp_enter(&tdx->vp, &tdx->vp_enter_args);
 
-	vt->exit_reason.full = tdx_to_vmx_exit_reason(vcpu);
+	vt->exit_reason = tdx_to_vmx_exit_reason(vcpu);
 
 	vt->exit_qualification = tdx->vp_enter_args.rcx;
 	tdx->ext_exit_qualification = tdx->vp_enter_args.rdx;
-- 
2.53.0