[PATCH v2 04/12] x86/x86: Add early_is_tdx_guest() interface

[Kuppuswamy Sathyanarayanan]

Add helper function to detect TDX feature support. It will be used
to protect TDX specific code in decompression code.

Reviewed-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Reviewed-by: Tony Luck <tony.luck@xxxxxxxxx>
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>
---

Changes since v1:
 * Removed is_tdx_guest() interface. We will rely on
   prot_guest_has(PR_GUEST_TDX) for TDX related checks.
 * Renamed is_tdx_guest() to early_is_tdx_guest() as per
   review suggestion.
 * Fixed commit title and log to reflect above changes.
 * Simplified native_cpuid_has_tdx_guest() as per review suggestion.

 arch/x86/boot/compressed/Makefile |  1 +
 arch/x86/boot/compressed/tdx.c    | 28 ++++++++++++++++++++++++++++
 2 files changed, 29 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 431bf7f846c3..22a2a6cc2ab4 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -98,6 +98,7 @@ 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..ddfa4a6d1939
--- /dev/null
+++ b/arch/x86/boot/compressed/tdx.c
@@ -0,0 +1,28 @@
+// 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, sig[3] = {0};
+
+	if (native_cpuid_eax(0) < TDX_CPUID_LEAF_ID)
+		return false;
+
+	native_cpuid(&eax, &sig[0], &sig[1], &sig[2]);
+
+	return !memcmp("IntelTDX    ", sig, 12);
+}
+
+bool early_is_tdx_guest(void)
+{
+	if (tdx_guest < 0)
+		tdx_guest = native_cpuid_has_tdx_guest();
+
+	return !!tdx_guest;
+}
-- 
2.25.1