linux-kernel - [PATCHv6, RESEND 4/4] x86/tdx: Enable CPU topology enumeration

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Message-ID: <20241104103803.195705-5-kirill.shutemov@linux.intel.com>
Date: Mon,  4 Nov 2024 12:38:03 +0200
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>
Cc: linux-coco@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	Kai Huang <kai.huang@...el.com>
Subject: [PATCHv6, RESEND 4/4] x86/tdx: Enable CPU topology enumeration

TDX 1.0 defines baseline behaviour of TDX guest platform. 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. 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. 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@...ux.intel.com>
Acked-by: Kai Huang <kai.huang@...el.com>
---
 arch/x86/coco/tdx/tdx.c           | 27 +++++++++++++++++++++++++++
 arch/x86/include/asm/shared/tdx.h |  2 ++
 2 files changed, 29 insertions(+)

diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
index a27230c44cc2..d4e7504aec19 100644
--- a/arch/x86/coco/tdx/tdx.c
+++ b/arch/x86/coco/tdx/tdx.c
@@ -250,6 +250,32 @@ static void disable_sept_ve(u64 td_attr)
 	return;
 }
 
+/*
+ * 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(void)
+{
+	u64 configured;
+
+	/* Has the VMM provided a valid topology configuration? */
+	tdg_vm_rd(TDCS_TOPOLOGY_ENUM_CONFIGURED, &configured);
+	if (!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 = {};
@@ -281,6 +307,7 @@ static void tdx_setup(u64 *cc_mask)
 	tdg_vm_wr(TDCS_NOTIFY_ENABLES, 0, -1ULL);
 
 	disable_sept_ve(td_attr);
+	enable_cpu_topology_enumeration();
 }
 
 /*
diff --git a/arch/x86/include/asm/shared/tdx.h b/arch/x86/include/asm/shared/tdx.h
index fecb2a6e864b..89f7fcade8ae 100644
--- a/arch/x86/include/asm/shared/tdx.h
+++ b/arch/x86/include/asm/shared/tdx.h
@@ -23,12 +23,14 @@
 #define TDCS_CONFIG_FLAGS		0x1110000300000016
 #define TDCS_TD_CTLS			0x1110000300000017
 #define TDCS_NOTIFY_ENABLES		0x9100000000000010
+#define TDCS_TOPOLOGY_ENUM_CONFIGURED	0x9100000000000019
 
 /* 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
-- 
2.45.2