[PATCHv2 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           | 19 +++++++++++++++++++
 arch/x86/include/asm/shared/tdx.h |  3 +++
 2 files changed, 22 insertions(+)

diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
index 860bfdd5a11d..b2d969432a22 100644
--- a/arch/x86/coco/tdx/tdx.c
+++ b/arch/x86/coco/tdx/tdx.c
@@ -289,6 +289,25 @@ static void tdx_setup(u64 *cc_mask)
 		else
 			tdx_panic(msg);
 	}
+
+	/*
+	 * 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 to the guest in a safe manner. 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.
+	 */
+	if ((features & TDX_FEATURES0_ENUM_TOPOLOGY) &&
+	    tdg_vm_rd(TDCS_TOPOLOGY_ENUM_CONFIGURED)) {
+		if (!tdcs_ctls_set(TD_CTLS_ENUM_TOPOLOGY))
+			pr_warn("Failed to enable ENUM_TOPOLOGY\n");
+	}
 }
 
 /*
diff --git a/arch/x86/include/asm/shared/tdx.h b/arch/x86/include/asm/shared/tdx.h
index 29a61c72e4dd..2964c506b241 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
 
 /* TDCS_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