[PATCH v14 08/22] KVM: selftests: Add TDX boot code

[Lisa Wang <wyihan@google.com>]

From: Erdem Aktas <erdemaktas@google.com>

Add code to boot a TDX test VM. Since TDX registers are inaccessible to
KVM, the boot code loads the relevant values from memory into the
registers before jumping to the guest code.

Reviewed-by: Binbin Wu <binbin.wu@linux.intel.com>
Signed-off-by: Erdem Aktas <erdemaktas@google.com>
Co-developed-by: Ackerley Tng <ackerleytng@google.com>
Signed-off-by: Ackerley Tng <ackerleytng@google.com>
Co-developed-by: Sagi Shahar <sagis@google.com>
Signed-off-by: Sagi Shahar <sagis@google.com>
Signed-off-by: Lisa Wang <wyihan@google.com>
---
 tools/testing/selftests/kvm/Makefile.kvm           |  1 +
 .../selftests/kvm/include/x86/tdx/td_boot.h        | 22 ++++++--
 tools/testing/selftests/kvm/lib/x86/tdx/td_boot.S  | 61 ++++++++++++++++++++++
 3 files changed, 81 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/kvm/Makefile.kvm b/tools/testing/selftests/kvm/Makefile.kvm
index 397afebbb34b..645d9aac61db 100644
--- a/tools/testing/selftests/kvm/Makefile.kvm
+++ b/tools/testing/selftests/kvm/Makefile.kvm
@@ -32,6 +32,7 @@ LIBKVM_x86 += lib/x86/svm.c
 LIBKVM_x86 += lib/x86/tdx/tdx_util.c
 LIBKVM_x86 += lib/x86/ucall.c
 LIBKVM_x86 += lib/x86/vmx.c
+LIBKVM_x86 += lib/x86/tdx/td_boot.S
 
 LIBKVM_arm64 += lib/arm64/gic.c
 LIBKVM_arm64 += lib/arm64/gic_v3.c
diff --git a/tools/testing/selftests/kvm/include/x86/tdx/td_boot.h b/tools/testing/selftests/kvm/include/x86/tdx/td_boot.h
index bf2282931d49..89cf6c3485be 100644
--- a/tools/testing/selftests/kvm/include/x86/tdx/td_boot.h
+++ b/tools/testing/selftests/kvm/include/x86/tdx/td_boot.h
@@ -2,9 +2,6 @@
 #ifndef SELFTEST_TDX_TD_BOOT_H
 #define SELFTEST_TDX_TD_BOOT_H
 
-#include <linux/compiler.h>
-#include <linux/types.h>
-
 /*
  * Layout for boot section (not to scale)
  *
@@ -24,7 +21,19 @@
  * |                           |
  * |                           |
  * |___________________________|____ 0x0_ffff_0000: TD_BOOT_PARAMETERS_GPA
+ *
+ * TD_BOOT_PARAMETERS_GPA is arbitrarily chosen to
+ *
+ * + be within the 4GB address space
+ * + provide enough contiguous memory for the struct td_boot_parameters such
+ *   that there is one struct td_per_vcpu_parameters for KVM_MAX_VCPUS
  */
+#define TD_BOOT_PARAMETERS_GPA 0xffff0000
+
+#if !defined(__ASSEMBLY__) && !defined(__ASSEMBLER__)
+
+#include <linux/compiler.h>
+#include <linux/types.h>
 
 /*
  * The exact memory layout for LGDT or LIDT instructions.
@@ -63,4 +72,11 @@ struct td_boot_parameters {
 	struct td_per_vcpu_parameters per_vcpu[];
 };
 
+void td_boot(void);
+void td_boot_code_end(void);
+
+#define TD_BOOT_CODE_SIZE (td_boot_code_end - td_boot)
+
+#endif /* !defined(__ASSEMBLY__) && !defined(__ASSEMBLER__) */
+
 #endif /* SELFTEST_TDX_TD_BOOT_H */
diff --git a/tools/testing/selftests/kvm/lib/x86/tdx/td_boot.S b/tools/testing/selftests/kvm/lib/x86/tdx/td_boot.S
new file mode 100644
index 000000000000..bca9a4c3d8f8
--- /dev/null
+++ b/tools/testing/selftests/kvm/lib/x86/tdx/td_boot.S
@@ -0,0 +1,61 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#include "tdx/td_boot.h"
+#include "tdx/td_boot_offsets.h"
+#include "processor_asm.h"
+
+.code32
+
+.globl td_boot
+td_boot:
+	/*
+	 * In this procedure, edi is used as a temporary register.
+	 * Paging is turned off.
+	 */
+	cli
+
+	movl $TD_BOOT_PARAMETERS_GPA, %ebx
+
+	/*
+	 * Find the address of struct td_per_vcpu_parameters for this
+	 * vCPU based on esi (TDX spec: initialized with vCPU id). Put
+	 * struct address into register for indirect addressing.
+	 */
+	movl $SIZEOF_TD_PER_VCPU_PARAMETERS, %eax
+	mul %esi
+	leal TD_BOOT_PARAMETERS_PER_VCPU(%ebx), %edi
+	addl %edi, %eax
+
+	/* Setup stack. */
+	movl TD_PER_VCPU_PARAMETERS_ESP_GVA(%eax), %esp
+
+	/* Setup GDT. */
+	leal TD_BOOT_PARAMETERS_GDT(%ebx), %edi
+	lgdt (%edi)
+
+	/* Setup IDT. */
+	leal TD_BOOT_PARAMETERS_IDT(%ebx), %edi
+	lidt (%edi)
+
+	/*
+	 * Set up control registers (There are no instructions to mov from
+	 * memory to control registers, hence use edi as a scratch register).
+	 */
+	movl TD_BOOT_PARAMETERS_CR4(%ebx), %edi
+	movl %edi, %cr4
+	movl TD_BOOT_PARAMETERS_CR3(%ebx), %edi
+	movl %edi, %cr3
+	movl TD_BOOT_PARAMETERS_CR0(%ebx), %edi
+	movl %edi, %cr0
+
+	/* Switching to 64bit mode after ljmp and then jump to guest code */
+	ljmp $(KERNEL_CS),$1f
+1:
+	jmp *TD_PER_VCPU_PARAMETERS_GUEST_CODE(%eax)
+
+/* Leave marker so size of td_boot code can be computed. */
+.globl td_boot_code_end
+td_boot_code_end:
+
+/* Disable executable stack. */
+.section .note.GNU-stack,"",%progbits

-- 
2.55.0.229.g6434b31f56-goog