[PATCHv3 4/4] x86/tdx: Enable ENUM_TOPOLOGY

[Kirill A. Shutemov]

TDX 1.0 defines baseline behaviour of TDX guest platform. In TDX 1.0
generates a #VE when accessing topology-related CPUID leafs (0xB and
0x1F) and the X2APIC_APICID MSR. The kernel returns all zeros on CPUID
topology. Any complications will cause problems.

The ENUM_TOPOLOGY feature allows the VMM to provide topology
information to the guest. Enabling the feature eliminates
topology-related #VEs: the TDX module virtualizes accesses to
the CPUID leafs and the MSR.

Enable ENUM_TOPOLOGY if it is available.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
 arch/x86/coco/tdx/tdx.c           | 32 +++++++++++++++++++++++++++++++
 arch/x86/include/asm/shared/tdx.h |  3 +++
 2 files changed, 35 insertions(+)

diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
index 6124d86e0b1d..23c507fa4057 100644
--- a/arch/x86/coco/tdx/tdx.c
+++ b/arch/x86/coco/tdx/tdx.c
@@ -249,6 +249,36 @@ static int try_to_disable_sept_ve(u64 features0, u64 td_attr)
 	return 0;
 }
 
+/*
+ * TDX 1.0 generates a #VE when accessing topology-related CPUID leafs (0xB and
+ * 0x1F) and the X2APIC_APICID MSR. The kernel returns all zeros on CPUID #VEs.
+ * In practice, this means that the kernel can only boot with a plain topology.
+ * Any complications will cause problems.
+ *
+ * The ENUM_TOPOLOGY feature allows the VMM to provide topology information.
+ * Enabling the feature  eliminates topology-related #VEs: the TDX module
+ * virtualizes accesses to the CPUID leafs and the MSR.
+ *
+ * Enable ENUM_TOPOLOGY if it is available.
+ */
+static void enable_cpu_topology_enumeration(u64 features0)
+{
+	u64 configured;
+
+	/* Does the TDX module support topology enumeration? */
+	if (!(features0 & TDX_FEATURES0_ENUM_TOPOLOGY))
+		return;
+
+	/* Has the VMM provided a valid topology configuration? */
+	if (tdg_vm_rd(TDCS_TOPOLOGY_ENUM_CONFIGURED, &configured) &&
+	    configured) {
+		pr_err("VMM did not configure X2APIC_IDs properly\n");
+		return;
+	}
+
+	tdg_vm_wr(TDCS_TD_CTLS, TD_CTLS_ENUM_TOPOLOGY, TD_CTLS_ENUM_TOPOLOGY);
+}
+
 static void tdx_setup(u64 *cc_mask)
 {
 	struct tdx_module_args args = {};
@@ -314,6 +344,8 @@ static void tdx_setup(u64 *cc_mask)
 		else
 			tdx_panic(msg);
 	}
+
+	enable_cpu_topology_enumeration(features0);
 }
 
 /*
diff --git a/arch/x86/include/asm/shared/tdx.h b/arch/x86/include/asm/shared/tdx.h
index 282497d2964b..08a9ef35d04e 100644
--- a/arch/x86/include/asm/shared/tdx.h
+++ b/arch/x86/include/asm/shared/tdx.h
@@ -27,15 +27,18 @@
 #define TDCS_CONFIG_FLAGS		0x1110000300000016
 #define TDCS_TD_CTLS			0x1110000300000017
 #define TDCS_NOTIFY_ENABLES		0x9100000000000010
+#define TDCS_TOPOLOGY_ENUM_CONFIGURED	0x9100000000000019
 
 /* TDX_FEATURES0 bits */
 #define TDX_FEATURES0_PENDING_EPT_VIOLATION_V2	BIT_ULL(16)
+#define TDX_FEATURES0_ENUM_TOPOLOGY		BIT_ULL(20)
 
 /* TDCS_CONFIG_FLAGS bits */
 #define TDCS_CONFIG_FLEXIBLE_PENDING_VE	BIT_ULL(1)
 
 /* TDCS_TD_CTLS bits */
 #define TD_CTLS_PENDING_VE_DISABLE	BIT_ULL(0)
+#define TD_CTLS_ENUM_TOPOLOGY		BIT_ULL(1)
 
 /* TDX hypercall Leaf IDs */
 #define TDVMCALL_MAP_GPA		0x10001
-- 
2.43.0