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Subject[PATCH v10 03/11] x86/cpufeatures: Add TDX Guest CPU feature
Date
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 v9:
* Added inline definition of is_tdx_guest() for !CONFIG_INTEL_TDX_GUEST case.

Changes since v8:
* Changed is_tdx_guest variable to is_tdx_guest() function.
* Added -fno-stack-protector and -pg for tdx.c
* Fixed tdx_early_init() related comments in x86_64_start_kernel()
as per review suggestion.

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 | 4 ++++
arch/x86/kernel/head64.c | 9 +++++++
arch/x86/kernel/tdx.c | 38 ++++++++++++++++++++++++++++++
5 files changed, 74 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..96ffce7bc530
--- /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
+
+bool is_tdx_guest(void);
+void __init tdx_early_init(void);
+
+#else
+
+static inline bool is_tdx_guest(void) { return false; }
+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 2ff3e600f426..8c9a9214dd34 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -22,6 +22,7 @@ CFLAGS_REMOVE_early_printk.o = -pg
CFLAGS_REMOVE_head64.o = -pg
CFLAGS_REMOVE_sev.o = -pg
CFLAGS_REMOVE_cc_platform.o = -pg
+CFLAGS_REMOVE_tdx.o = -pg
endif

KASAN_SANITIZE_head$(BITS).o := n
@@ -31,6 +32,7 @@ KASAN_SANITIZE_stacktrace.o := n
KASAN_SANITIZE_paravirt.o := n
KASAN_SANITIZE_sev.o := n
KASAN_SANITIZE_cc_platform.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.
@@ -50,6 +52,7 @@ KCOV_INSTRUMENT := n

CFLAGS_head$(BITS).o += -fno-stack-protector
CFLAGS_cc_platform.o += -fno-stack-protector
+CFLAGS_tdx.o += -fno-stack-protector

CFLAGS_irq.o := -I $(srctree)/$(src)/../include/asm/trace

@@ -130,6 +133,7 @@ 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 fc5371a7e9d1..a5ee90df2aba 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.
@@ -500,6 +501,14 @@ asmlinkage __visible void __init x86_64_start_kernel(char * real_mode_data)

copy_bootdata(__va(real_mode_data));

+ /*
+ * A future dependency on cmdline parameters is expected (for
+ * adding debug options). 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..88bf12788684
--- /dev/null
+++ b/arch/x86/kernel/tdx.c
@@ -0,0 +1,38 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (C) 2020 Intel Corporation */
+
+#undef pr_fmt
+#define pr_fmt(fmt) "tdx: " fmt
+
+#include <asm/tdx.h>
+
+bool is_tdx_guest(void)
+{
+ static int tdx_guest = -1;
+ u32 eax, sig[3];
+
+ if (tdx_guest >= 0)
+ goto done;
+
+ if (cpuid_eax(0) < TDX_CPUID_LEAF_ID) {
+ tdx_guest = 0;
+ goto done;
+ }
+
+ cpuid_count(TDX_CPUID_LEAF_ID, 0, &eax, &sig[0], &sig[2], &sig[1]);
+
+ tdx_guest = !memcmp("IntelTDX ", sig, 12);
+
+done:
+ return !!tdx_guest;
+}
+
+void __init tdx_early_init(void)
+{
+ if (!is_tdx_guest())
+ return;
+
+ setup_force_cpu_cap(X86_FEATURE_TDX_GUEST);
+
+ pr_info("Guest initialized\n");
+}
--
2.25.1
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