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Subject[RFC v1 03/26] x86/cpufeatures: Add is_tdx_guest() interface
Date
Add helper function to detect TDX feature support. It will be used
to protect TDX specific code.

Co-developed-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
---
arch/x86/boot/compressed/Makefile | 1 +
arch/x86/boot/compressed/tdx.c | 32 +++++++++++++++++++++++++++++++
arch/x86/include/asm/tdx.h | 8 ++++++++
arch/x86/kernel/tdx.c | 6 ++++++
4 files changed, 47 insertions(+)
create mode 100644 arch/x86/boot/compressed/tdx.c

diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
index e0bc3988c3fa..a2554621cefe 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -96,6 +96,7 @@ ifdef CONFIG_X86_64
endif

vmlinux-objs-$(CONFIG_ACPI) += $(obj)/acpi.o
+vmlinux-objs-$(CONFIG_INTEL_TDX_GUEST) += $(obj)/tdx.o

vmlinux-objs-$(CONFIG_EFI_MIXED) += $(obj)/efi_thunk_$(BITS).o
efi-obj-$(CONFIG_EFI_STUB) = $(objtree)/drivers/firmware/efi/libstub/lib.a
diff --git a/arch/x86/boot/compressed/tdx.c b/arch/x86/boot/compressed/tdx.c
new file mode 100644
index 000000000000..0a87c1775b67
--- /dev/null
+++ b/arch/x86/boot/compressed/tdx.c
@@ -0,0 +1,32 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * tdx.c - Early boot code for TDX
+ */
+
+#include <asm/tdx.h>
+
+static int __ro_after_init tdx_guest = -1;
+
+static inline bool native_cpuid_has_tdx_guest(void)
+{
+ u32 eax = TDX_CPUID_LEAF_ID, signature[3] = {0};
+
+ if (native_cpuid_eax(0) < TDX_CPUID_LEAF_ID)
+ return false;
+
+ native_cpuid(&eax, &signature[0], &signature[1], &signature[2]);
+
+ if (memcmp("IntelTDX ", signature, 12))
+ return false;
+
+ return true;
+}
+
+bool is_tdx_guest(void)
+{
+ if (tdx_guest < 0)
+ tdx_guest = native_cpuid_has_tdx_guest();
+
+ return !!tdx_guest;
+}
+
diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
index 2cc246c0cecf..0b9d571b1f95 100644
--- a/arch/x86/include/asm/tdx.h
+++ b/arch/x86/include/asm/tdx.h
@@ -7,10 +7,18 @@

#ifdef CONFIG_INTEL_TDX_GUEST

+/* Common API to check TDX support in decompression and common kernel code. */
+bool is_tdx_guest(void);
+
void __init tdx_early_init(void);

#else // !CONFIG_INTEL_TDX_GUEST

+static inline bool is_tdx_guest(void)
+{
+ return false;
+}
+
static inline void tdx_early_init(void) { };

#endif /* CONFIG_INTEL_TDX_GUEST */
diff --git a/arch/x86/kernel/tdx.c b/arch/x86/kernel/tdx.c
index 473b4c1c0920..e44e55d1e519 100644
--- a/arch/x86/kernel/tdx.c
+++ b/arch/x86/kernel/tdx.c
@@ -20,6 +20,12 @@ static inline bool cpuid_has_tdx_guest(void)
return true;
}

+bool is_tdx_guest(void)
+{
+ return static_cpu_has(X86_FEATURE_TDX_GUEST);
+}
+EXPORT_SYMBOL_GPL(is_tdx_guest);
+
void __init tdx_early_init(void)
{
if (!cpuid_has_tdx_guest())
--
2.25.1
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