[PATCH v7 02/10] x86/tdx: Add early_is_tdx_guest() interface

Kuppuswamy Sathyanarayanan
2021-10-05T20:42:06Z

Add helper function to detect TDX feature support. It will be used
to protect TDX specific code in decompression code (for example to
add TDX specific I/O fixes in decompression code).

Reviewed-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
---

Changes since v6:
* None

Changes since v5:
* None

Changes since v4:
* None

Changes since v3:
* None

Changes since v2:
* Fixed string order issue in cpuid_count() call.

Changes since v1:
* Modified cpuid_has_tdx_guest() to use cpuid_count() instead of native_cpuid().
* Reused cpuid_count() from cpuflags.c.
* Added a new function cpuid_eax().
* Renamed native_cpuid_has_tdx_guest() as early_cpuid_has_tdx_guest().

arch/x86/boot/compressed/Makefile | 1 +
arch/x86/boot/compressed/tdx.c | 31 +++++++++++++++++++++++++++++++
arch/x86/boot/cpuflags.c | 12 ++++++++++--
arch/x86/boot/cpuflags.h | 2 ++
4 files changed, 44 insertions(+), 2 deletions(-)
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..ecb3b42992e0
--- /dev/null
+++ b/arch/x86/boot/compressed/tdx.c
@@ -0,0 +1,31 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * tdx.c - Early boot code for TDX
+ */
+
+#include "../cpuflags.h"
+#include "../string.h"
+
+#define TDX_CPUID_LEAF_ID 0x21
+
+static int tdx_guest = -1;
+
+static inline bool early_cpuid_has_tdx_guest(void)
+{
+ u32 eax = TDX_CPUID_LEAF_ID, sig[3] = {0};
+
+ 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);
+}
+
+bool early_is_tdx_guest(void)
+{
+ if (tdx_guest < 0)
+ tdx_guest = early_cpuid_has_tdx_guest();
+
+ return !!tdx_guest;
+}
diff --git a/arch/x86/boot/cpuflags.c b/arch/x86/boot/cpuflags.c
index a0b75f73dc63..102613a092aa 100644
--- a/arch/x86/boot/cpuflags.c
+++ b/arch/x86/boot/cpuflags.c
@@ -71,8 +71,7 @@ int has_eflag(unsigned long mask)
# define EBX_REG "=b"
#endif

-static inline void cpuid_count(u32 id, u32 count,
- u32 *a, u32 *b, u32 *c, u32 *d)
+void cpuid_count(u32 id, u32 count, u32 *a, u32 *b, u32 *c, u32 *d)
{
asm volatile(".ifnc %%ebx,%3 ; movl %%ebx,%3 ; .endif \n\t"
"cpuid \n\t"
@@ -82,6 +81,15 @@ static inline void cpuid_count(u32 id, u32 count,
);
}

+u32 cpuid_eax(u32 id)
+{
+ u32 eax, ebx, ecx, edx;
+
+ cpuid_count(id, 0, &eax, &ebx, &ecx, &edx);
+
+ return eax;
+}
+
#define cpuid(id, a, b, c, d) cpuid_count(id, 0, a, b, c, d)

void get_cpuflags(void)
diff --git a/arch/x86/boot/cpuflags.h b/arch/x86/boot/cpuflags.h
index 2e20814d3ce3..5a72233eb8fd 100644
--- a/arch/x86/boot/cpuflags.h
+++ b/arch/x86/boot/cpuflags.h
@@ -17,5 +17,7 @@ extern u32 cpu_vendor[3];

int has_eflag(unsigned long mask);
void get_cpuflags(void);
+void cpuid_count(u32 id, u32 count, u32 *a, u32 *b, u32 *c, u32 *d);
+u32 cpuid_eax(u32 id);

#endif
--
2.25.1