[PATCH v11 09/21] KVM: selftests: Set up TDX boot code region

Sagi Shahar
2025-09-25T17:29:15Z

Add memory for TDX boot code in a separate memslot.

Use virt_map() to get identity map in this memory region to allow for
seamless transition from paging disabled to paging enabled code.

Copy the boot code into the memory region and set up the reset vector
at this point. While it's possible to separate the memory allocation and
boot code initialization into separate functions, having all the
calculations for memory size and offsets in one place simplifies the
code and avoids duplications.

Handcode the reset vector as suggested by Sean Christopherson.

Reviewed-by: Binbin Wu <binbin.wu@linux.intel.com>
Suggested-by: Sean Christopherson <seanjc@google.com>
Co-developed-by: Erdem Aktas <erdemaktas@google.com>
Signed-off-by: Erdem Aktas <erdemaktas@google.com>
Signed-off-by: Sagi Shahar <sagis@google.com>
---
tools/testing/selftests/kvm/Makefile.kvm | 1 +
.../selftests/kvm/include/x86/tdx/tdx_util.h | 2 +
.../selftests/kvm/lib/x86/tdx/tdx_util.c | 54 +++++++++++++++++++
3 files changed, 57 insertions(+)
create mode 100644 tools/testing/selftests/kvm/lib/x86/tdx/tdx_util.c

diff --git a/tools/testing/selftests/kvm/Makefile.kvm b/tools/testing/selftests/kvm/Makefile.kvm
index d11d02e17cc5..52c90f1c0484 100644
--- a/tools/testing/selftests/kvm/Makefile.kvm
+++ b/tools/testing/selftests/kvm/Makefile.kvm
@@ -31,6 +31,7 @@ LIBKVM_x86 += lib/x86/sev.c
LIBKVM_x86 += lib/x86/svm.c
LIBKVM_x86 += lib/x86/ucall.c
LIBKVM_x86 += lib/x86/vmx.c
+LIBKVM_x86 += lib/x86/tdx/tdx_util.c
LIBKVM_x86 += lib/x86/tdx/td_boot.S

LIBKVM_arm64 += lib/arm64/gic.c
diff --git a/tools/testing/selftests/kvm/include/x86/tdx/tdx_util.h b/tools/testing/selftests/kvm/include/x86/tdx/tdx_util.h
index 286d5e3c24b1..ec05bcd59145 100644
--- a/tools/testing/selftests/kvm/include/x86/tdx/tdx_util.h
+++ b/tools/testing/selftests/kvm/include/x86/tdx/tdx_util.h
@@ -11,4 +11,6 @@ static inline bool is_tdx_vm(struct kvm_vm *vm)
return vm->type == KVM_X86_TDX_VM;
}

+void vm_tdx_setup_boot_code_region(struct kvm_vm *vm);
+
#endif // SELFTESTS_TDX_TDX_UTIL_H
diff --git a/tools/testing/selftests/kvm/lib/x86/tdx/tdx_util.c b/tools/testing/selftests/kvm/lib/x86/tdx/tdx_util.c
new file mode 100644
index 000000000000..a1cf12de9d56
--- /dev/null
+++ b/tools/testing/selftests/kvm/lib/x86/tdx/tdx_util.c
@@ -0,0 +1,54 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <stdint.h>
+
+#include "kvm_util.h"
+#include "processor.h"
+#include "tdx/td_boot.h"
+#include "tdx/tdx_util.h"
+
+/* Arbitrarily selected to avoid overlaps with anything else */
+#define TD_BOOT_CODE_SLOT 20
+
+#define X86_RESET_VECTOR 0xfffffff0ul
+#define X86_RESET_VECTOR_SIZE 16
+
+void vm_tdx_setup_boot_code_region(struct kvm_vm *vm)
+{
+ size_t total_code_size = TD_BOOT_CODE_SIZE + X86_RESET_VECTOR_SIZE;
+ vm_paddr_t boot_code_gpa = X86_RESET_VECTOR - TD_BOOT_CODE_SIZE;
+ vm_paddr_t alloc_gpa = round_down(boot_code_gpa, PAGE_SIZE);
+ size_t nr_pages = DIV_ROUND_UP(total_code_size, PAGE_SIZE);
+ vm_paddr_t gpa;
+ uint8_t *hva;
+
+ vm_userspace_mem_region_add(vm, VM_MEM_SRC_ANONYMOUS,
+ alloc_gpa,
+ TD_BOOT_CODE_SLOT, nr_pages,
+ KVM_MEM_GUEST_MEMFD);
+
+ gpa = vm_phy_pages_alloc(vm, nr_pages, alloc_gpa, TD_BOOT_CODE_SLOT);
+ TEST_ASSERT(gpa == alloc_gpa, "Failed vm_phy_pages_alloc\n");
+
+ virt_map(vm, alloc_gpa, alloc_gpa, nr_pages);
+ hva = addr_gpa2hva(vm, boot_code_gpa);
+ memcpy(hva, td_boot, TD_BOOT_CODE_SIZE);
+
+ hva += TD_BOOT_CODE_SIZE;
+ TEST_ASSERT(hva == addr_gpa2hva(vm, X86_RESET_VECTOR),
+ "Expected RESET vector at hva 0x%lx, got %lx",
+ (unsigned long)addr_gpa2hva(vm, X86_RESET_VECTOR), (unsigned long)hva);
+
+ /*
+ * Handcode "JMP rel8" at the RESET vector to jump back to the TD boot
+ * code, as there are only 16 bytes at the RESET vector before RIP will
+ * wrap back to zero. Insert a trailing int3 so that the vCPU crashes
+ * in case the JMP somehow falls through. Note! The target address is
+ * relative to the end of the instruction!
+ */
+ TEST_ASSERT(TD_BOOT_CODE_SIZE + 2 <= 128,
+ "TD boot code not addressable by 'JMP rel8'");
+ hva[0] = 0xeb;
+ hva[1] = 256 - 2 - TD_BOOT_CODE_SIZE;
+ hva[2] = 0xcc;
+}
--
2.51.0.536.g15c5d4f767-goog