[PATCH v11 07/21] KVM: selftests: Define structs to pass parameters to TDX boot code

Sagi Shahar
2025-09-25T17:29:11Z

TDX registers are inaccessible to KVM. Therefore we need a different
mechanism to load boot parameters for TDX code. TDX boot code will read
the registers values from memory and set the registers manually.

This patch defines the data structures used to communicate between c
code and the TDX assembly boot code which will be added in a later
patch.

Use kbuild.h to expose the offsets into the structs from c code to
assembly code.

Reviewed-by: Binbin Wu <binbin.wu@linux.intel.com>
Co-developed-by: Ackerley Tng <ackerleytng@google.com>
Signed-off-by: Ackerley Tng <ackerleytng@google.com>
Signed-off-by: Sagi Shahar <sagis@google.com>
---
tools/testing/selftests/kvm/Makefile.kvm | 18 +++++
.../selftests/kvm/include/x86/tdx/td_boot.h | 69 +++++++++++++++++++
.../kvm/lib/x86/tdx/td_boot_offsets.c | 21 ++++++
3 files changed, 108 insertions(+)
create mode 100644 tools/testing/selftests/kvm/include/x86/tdx/td_boot.h
create mode 100644 tools/testing/selftests/kvm/lib/x86/tdx/td_boot_offsets.c

diff --git a/tools/testing/selftests/kvm/Makefile.kvm b/tools/testing/selftests/kvm/Makefile.kvm
index 41b40c676d7f..3f93c093b046 100644
--- a/tools/testing/selftests/kvm/Makefile.kvm
+++ b/tools/testing/selftests/kvm/Makefile.kvm
@@ -19,6 +19,8 @@ LIBKVM += lib/userfaultfd_util.c

LIBKVM_STRING += lib/string_override.c

+LIBKVM_ASM_DEFS += lib/x86/tdx/td_boot_offsets.c
+
LIBKVM_x86 += lib/x86/apic.c
LIBKVM_x86 += lib/x86/handlers.S
LIBKVM_x86 += lib/x86/hyperv.c
@@ -230,6 +232,10 @@ OVERRIDE_TARGETS = 1
include ../lib.mk
include ../cgroup/lib/libcgroup.mk

+# Enable Kbuild tools.
+include $(top_srcdir)/scripts/Kbuild.include
+include $(top_srcdir)/scripts/Makefile.lib
+
INSTALL_HDR_PATH = $(top_srcdir)/usr
LINUX_HDR_PATH = $(INSTALL_HDR_PATH)/include/
LINUX_TOOL_INCLUDE = $(top_srcdir)/tools/include
@@ -282,6 +288,7 @@ LIBKVM_S := $(filter %.S,$(LIBKVM))
LIBKVM_C_OBJ := $(patsubst %.c, $(OUTPUT)/%.o, $(LIBKVM_C))
LIBKVM_S_OBJ := $(patsubst %.S, $(OUTPUT)/%.o, $(LIBKVM_S))
LIBKVM_STRING_OBJ := $(patsubst %.c, $(OUTPUT)/%.o, $(LIBKVM_STRING))
+LIBKVM_ASM_DEFS_OBJ += $(patsubst %.c, $(OUTPUT)/%.s, $(LIBKVM_ASM_DEFS))
LIBKVM_OBJS = $(LIBKVM_C_OBJ) $(LIBKVM_S_OBJ) $(LIBKVM_STRING_OBJ) $(LIBCGROUP_O)
SPLIT_TEST_GEN_PROGS := $(patsubst %, $(OUTPUT)/%, $(SPLIT_TESTS))
SPLIT_TEST_GEN_OBJ := $(patsubst %, $(OUTPUT)/$(ARCH)/%.o, $(SPLIT_TESTS))
@@ -308,6 +315,7 @@ $(SPLIT_TEST_GEN_OBJ): $(OUTPUT)/$(ARCH)/%.o: $(ARCH)/%.c

EXTRA_CLEAN += $(GEN_HDRS) \
$(LIBKVM_OBJS) \
+ $(LIBKVM_ASM_DEFS_OBJ) \
$(SPLIT_TEST_GEN_OBJ) \
$(TEST_DEP_FILES) \
$(TEST_GEN_OBJ) \
@@ -319,18 +327,28 @@ $(LIBKVM_C_OBJ): $(OUTPUT)/%.o: %.c $(GEN_HDRS)
$(LIBKVM_S_OBJ): $(OUTPUT)/%.o: %.S $(GEN_HDRS)
$(CC) $(CFLAGS) $(CPPFLAGS) $(TARGET_ARCH) -c $< -o $@

+$(LIBKVM_ASM_DEFS_OBJ): $(OUTPUT)/%.s: %.c FORCE
+ $(CC) $(CFLAGS) $(CPPFLAGS) $(TARGET_ARCH) -S $< -o $@
+
# Compile the string overrides as freestanding to prevent the compiler from
# generating self-referential code, e.g. without "freestanding" the compiler may
# "optimize" memcmp() by invoking memcmp(), thus causing infinite recursion.
$(LIBKVM_STRING_OBJ): $(OUTPUT)/%.o: %.c
$(CC) $(CFLAGS) $(CPPFLAGS) $(TARGET_ARCH) -c -ffreestanding $< -o $@

+$(OUTPUT)/include/x86/tdx/td_boot_offsets.h: $(OUTPUT)/lib/x86/tdx/td_boot_offsets.s FORCE
+ $(call filechk,offsets,__TDX_BOOT_OFFSETS_H__)
+
+EXTRA_CLEAN += $(OUTPUT)/include/x86/tdx/td_boot_offsets.h
+
$(shell mkdir -p $(sort $(dir $(TEST_GEN_PROGS))))
$(SPLIT_TEST_GEN_OBJ): $(GEN_HDRS)
$(TEST_GEN_PROGS): $(LIBKVM_OBJS)
$(TEST_GEN_PROGS_EXTENDED): $(LIBKVM_OBJS)
$(TEST_GEN_OBJ): $(GEN_HDRS)

+FORCE:
+
cscope: include_paths = $(LINUX_TOOL_INCLUDE) $(LINUX_HDR_PATH) include lib ..
cscope:
$(RM) cscope.*
diff --git a/tools/testing/selftests/kvm/include/x86/tdx/td_boot.h b/tools/testing/selftests/kvm/include/x86/tdx/td_boot.h
new file mode 100644
index 000000000000..32631645fe13
--- /dev/null
+++ b/tools/testing/selftests/kvm/include/x86/tdx/td_boot.h
@@ -0,0 +1,69 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef SELFTEST_TDX_TD_BOOT_H
+#define SELFTEST_TDX_TD_BOOT_H
+
+#include <stdint.h>
+
+#include <linux/compiler.h>
+#include <linux/sizes.h>
+
+/*
+ * Layout for boot section (not to scale)
+ *
+ * GPA
+ * _________________________________ 0x1_0000_0000 (4GB)
+ * | Boot code trampoline |
+ * |___________________________|____ 0x0_ffff_fff0: Reset vector (16B below 4GB)
+ * | Boot code |
+ * |___________________________|____ td_boot will be copied here, so that the
+ * | | jmp to td_boot is exactly at the reset vector
+ * | Empty space |
+ * | |
+ * |───────────────────────────|
+ * | |
+ * | |
+ * | Boot parameters |
+ * | |
+ * | |
+ * |___________________________|____ 0x0_ffff_0000: TD_BOOT_PARAMETERS_GPA
+ */
+#define FOUR_GIGABYTES_GPA (SZ_4G)
+
+/*
+ * The exact memory layout for LGDT or LIDT instructions.
+ */
+struct __packed td_boot_parameters_dtr {
+ uint16_t limit;
+ uint32_t base;
+};
+
+/*
+ * Allows each vCPU to be initialized with different rip and esp.
+ */
+struct td_per_vcpu_parameters {
+ uint32_t esp_gva;
+ uint64_t guest_code;
+};
+
+/*
+ * Boot parameters for the TD.
+ *
+ * Unlike a regular VM, KVM cannot set registers such as esp, eip, etc
+ * before boot, so to run selftests, these registers' values have to be
+ * initialized by the TD.
+ *
+ * This struct is loaded in TD private memory at TD_BOOT_PARAMETERS_GPA.
+ *
+ * The TD boot code will read off parameters from this struct and set up the
+ * vCPU for executing selftests.
+ */
+struct td_boot_parameters {
+ uint32_t cr0;
+ uint32_t cr3;
+ uint32_t cr4;
+ struct td_boot_parameters_dtr gdtr;
+ struct td_boot_parameters_dtr idtr;
+ struct td_per_vcpu_parameters per_vcpu[];
+};
+
+#endif /* SELFTEST_TDX_TD_BOOT_H */
diff --git a/tools/testing/selftests/kvm/lib/x86/tdx/td_boot_offsets.c b/tools/testing/selftests/kvm/lib/x86/tdx/td_boot_offsets.c
new file mode 100644
index 000000000000..7f76a3585b99
--- /dev/null
+++ b/tools/testing/selftests/kvm/lib/x86/tdx/td_boot_offsets.c
@@ -0,0 +1,21 @@
+// SPDX-License-Identifier: GPL-2.0
+#define COMPILE_OFFSETS
+
+#include <linux/kbuild.h>
+
+#include "tdx/td_boot.h"
+
+static void __attribute__((used)) common(void)
+{
+ OFFSET(TD_BOOT_PARAMETERS_CR0, td_boot_parameters, cr0);
+ OFFSET(TD_BOOT_PARAMETERS_CR3, td_boot_parameters, cr3);
+ OFFSET(TD_BOOT_PARAMETERS_CR4, td_boot_parameters, cr4);
+ OFFSET(TD_BOOT_PARAMETERS_GDT, td_boot_parameters, gdtr);
+ OFFSET(TD_BOOT_PARAMETERS_IDT, td_boot_parameters, idtr);
+ OFFSET(TD_BOOT_PARAMETERS_PER_VCPU, td_boot_parameters, per_vcpu);
+ OFFSET(TD_PER_VCPU_PARAMETERS_ESP_GVA, td_per_vcpu_parameters, esp_gva);
+ OFFSET(TD_PER_VCPU_PARAMETERS_GUEST_CODE, td_per_vcpu_parameters,
+ guest_code);
+ DEFINE(SIZEOF_TD_PER_VCPU_PARAMETERS,
+ sizeof(struct td_per_vcpu_parameters));
+}
--
2.51.0.536.g15c5d4f767-goog