[PATCH v5 03/12] x86/cpufeatures: Add TDX Guest CPU feature

Kuppuswamy Sathyanarayanan
2021-08-04T18:14:53Z

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@linux.intel.com>
---

Changes since v4:
* Moved tdx_early_init() below copy_bootdata() because of
cmdline and IDT dependencies.

Changes since v3:
* Fixed order of string cpuid_count() call.

Changes since v2:
* Fixed debug prints as per Borislav suggestion.

Changes since v1:
* Fixed commit log issues reported by Borislav.
* Moved header file include to the start of tdx.h.
* Added pr_fmt for TDX.
* Simplified cpuid_has_tdx_guest() implementation as per
Borislav comments.

arch/x86/include/asm/cpufeatures.h | 1 +
arch/x86/include/asm/tdx.h | 20 ++++++++++++++++++++
arch/x86/kernel/Makefile | 1 +
arch/x86/kernel/head64.c | 3 +++
arch/x86/kernel/tdx.c | 29 +++++++++++++++++++++++++++++
5 files changed, 54 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..c738bde944d1
--- /dev/null
+++ b/arch/x86/include/asm/tdx.h
@@ -0,0 +1,20 @@
+/* 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
+
+void __init tdx_early_init(void);
+
+#else
+
+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 3e625c61f008..b49110bd50d9 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -127,6 +127,7 @@ 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 de01903c3735..f41f3dac1318 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 +496,8 @@ asmlinkage __visible void __init x86_64_start_kernel(char * real_mode_data)

copy_bootdata(__va(real_mode_data));

+ 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..39dd1515b131
--- /dev/null
+++ b/arch/x86/kernel/tdx.c
@@ -0,0 +1,29 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (C) 2020 Intel Corporation */
+
+#undef pr_fmt
+#define pr_fmt(fmt) "x86/tdx: " fmt
+
+#include <asm/tdx.h>
+
+static inline bool cpuid_has_tdx_guest(void)
+{
+ u32 eax, sig[3];
+
+ if (cpuid_eax(0) < TDX_CPUID_LEAF_ID)
+ return false;
+
+ cpuid_count(TDX_CPUID_LEAF_ID, 0, &eax, &sig[0], &sig[2], &sig[1]);
+
+ return !memcmp("IntelTDX ", sig, 12);
+}
+
+void __init tdx_early_init(void)
+{
+ if (!cpuid_has_tdx_guest())
+ return;
+
+ setup_force_cpu_cap(X86_FEATURE_TDX_GUEST);
+
+ pr_info("Guest initialized\n");
+}
--
2.25.1