[PATCH v8 03/11] x86/cpufeatures: Add TDX Guest CPU feature

[Kuppuswamy Sathyanarayanan]

Add CPU feature detection for Trusted Domain Extensions support. TDX
feature adds capabilities to keep guest register state and memory
isolated from hypervisor.

For TDX guest platforms, executing CPUID(eax=0x21, ecx=0) will return
following values in EAX, EBX, ECX and EDX.

EAX:  Maximum sub-leaf number:  0
EBX/EDX/ECX:  Vendor string:

EBX =  "Inte"
EDX =  "lTDX"
ECX =  "    "

So when above condition is true, set X86_FEATURE_TDX_GUEST feature cap
bit.

Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>
---

Changes since v7:
 * Add comments for the order of tdx_early_init() call.
 * Similar to AMD (sme_me_mask) added a global variable
   is_tdx_guest for Intel TDX related checks.
 * Changed pr_fmt from "x86/tdx: " to "tdx:"

 arch/x86/include/asm/cpufeatures.h |  1 +
 arch/x86/include/asm/tdx.h         | 22 ++++++++++++++++
 arch/x86/kernel/Makefile           |  2 ++
 arch/x86/kernel/head64.c           |  8 ++++++
 arch/x86/kernel/tdx.c              | 40 ++++++++++++++++++++++++++++++
 5 files changed, 73 insertions(+)
 create mode 100644 arch/x86/include/asm/tdx.h
 create mode 100644 arch/x86/kernel/tdx.c

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index d0ce5cfd3ac1..84997abeb401 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -238,6 +238,7 @@
 #define X86_FEATURE_VMW_VMMCALL		( 8*32+19) /* "" VMware prefers VMMCALL hypercall instruction */
 #define X86_FEATURE_PVUNLOCK		( 8*32+20) /* "" PV unlock function */
 #define X86_FEATURE_VCPUPREEMPT		( 8*32+21) /* "" PV vcpu_is_preempted function */
+#define X86_FEATURE_TDX_GUEST		( 8*32+22) /* Trusted Domain Extensions Guest */
 
 /* Intel-defined CPU features, CPUID level 0x00000007:0 (EBX), word 9 */
 #define X86_FEATURE_FSGSBASE		( 9*32+ 0) /* RDFSBASE, WRFSBASE, RDGSBASE, WRGSBASE instructions*/
diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
new file mode 100644
index 000000000000..d552c7248bc7
--- /dev/null
+++ b/arch/x86/include/asm/tdx.h
@@ -0,0 +1,22 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright (C) 2020 Intel Corporation */
+#ifndef _ASM_X86_TDX_H
+#define _ASM_X86_TDX_H
+
+#include <linux/cpufeature.h>
+
+#define TDX_CPUID_LEAF_ID	0x21
+
+#ifdef CONFIG_INTEL_TDX_GUEST
+
+extern u64 is_tdx_guest;
+void __init tdx_early_init(void);
+
+#else
+
+#define is_tdx_guest		0ULL
+static inline void tdx_early_init(void) { };
+
+#endif /* CONFIG_INTEL_TDX_GUEST */
+
+#endif /* _ASM_X86_TDX_H */
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index f91403a78594..159fccfece65 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -29,6 +29,7 @@ KASAN_SANITIZE_dumpstack_$(BITS).o			:= n
 KASAN_SANITIZE_stacktrace.o				:= n
 KASAN_SANITIZE_paravirt.o				:= n
 KASAN_SANITIZE_sev.o					:= n
+KASAN_SANITIZE_tdx.o					:= n
 
 # With some compiler versions the generated code results in boot hangs, caused
 # by several compilation units. To be safe, disable all instrumentation.
@@ -127,6 +128,7 @@ obj-$(CONFIG_PARAVIRT_CLOCK)	+= pvclock.o
 obj-$(CONFIG_X86_PMEM_LEGACY_DEVICE) += pmem.o
 
 obj-$(CONFIG_JAILHOUSE_GUEST)	+= jailhouse.o
+obj-$(CONFIG_INTEL_TDX_GUEST)	+= tdx.o
 
 obj-$(CONFIG_EISA)		+= eisa.o
 obj-$(CONFIG_PCSPKR_PLATFORM)	+= pcspeaker.o
diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index f98c76a1d16c..97ce0d037387 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -40,6 +40,7 @@
 #include <asm/extable.h>
 #include <asm/trapnr.h>
 #include <asm/sev.h>
+#include <asm/tdx.h>
 
 /*
  * Manage page tables very early on.
@@ -495,6 +496,13 @@ asmlinkage __visible void __init x86_64_start_kernel(char * real_mode_data)
 
 	copy_bootdata(__va(real_mode_data));
 
+	/*
+	 * tdx_early_init() has dependency on command line parameters.
+	 * So the order of calling it should be after copy_bootdata()
+	 * (in which command line parameter is initialized).
+	 */
+	tdx_early_init();
+
 	/*
 	 * Load microcode early on BSP.
 	 */
diff --git a/arch/x86/kernel/tdx.c b/arch/x86/kernel/tdx.c
new file mode 100644
index 000000000000..ad3ff5925153
--- /dev/null
+++ b/arch/x86/kernel/tdx.c
@@ -0,0 +1,40 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (C) 2020 Intel Corporation */
+
+#undef pr_fmt
+#define pr_fmt(fmt)     "tdx: " fmt
+
+#include <asm/tdx.h>
+
+/*
+ * Allocate it in the data region to avoid zeroing it during
+ * BSS initialization. It is mainly used in cc_platform_has()
+ * call during early boot call.
+ */
+u64 __section(".data") is_tdx_guest = 0;
+
+static void __init is_tdx_guest_init(void)
+{
+	u32 eax, sig[3];
+
+	if (cpuid_eax(0) < TDX_CPUID_LEAF_ID) {
+		is_tdx_guest = 0;
+		return;
+	}
+
+	cpuid_count(TDX_CPUID_LEAF_ID, 0, &eax, &sig[0], &sig[2], &sig[1]);
+
+	is_tdx_guest = !memcmp("IntelTDX    ", sig, 12);
+}
+
+void __init tdx_early_init(void)
+{
+	is_tdx_guest_init();
+
+	if (!is_tdx_guest)
+		return;
+
+	setup_force_cpu_cap(X86_FEATURE_TDX_GUEST);
+
+	pr_info("Guest initialized\n");
+}
-- 
2.25.1