On 8/12/2025 4:13 AM, Sean Christopherson wrote:
On Thu, Aug 07, 2025, Sagi Shahar wrote:
[...]
+
+/*
+ * 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 __packed td_boot_parameters {
None of these comments explain why these structures are __packed, and I suspect
_that_ is the most interesting/relevant information for unfamiliar readers.
I guess because the fields defined in this structure are accessed by hard-coded
offsets in boot code.
But as you suggested below, replicating the functionality of the kernel's
OFFSET() could get rid of "__packed".
A side topic is when developers should provide comments for the uses of
"__packed". Is it always preferred a comment for it or a developer can save
the comment for obvious cases, e.g, the structure is defined according to
some hardware layout?
+ 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[];
+};
+
...
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..c8cbe214bba9
--- /dev/null
+++ b/tools/testing/selftests/kvm/lib/x86/tdx/td_boot.S
@@ -0,0 +1,100 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#include "tdx/td_boot_asm.h"
+
+/* Offsets for reading struct td_boot_parameters. */
+#define TD_BOOT_PARAMETERS_CR0 0
+#define TD_BOOT_PARAMETERS_CR3 4
+#define TD_BOOT_PARAMETERS_CR4 8
+#define TD_BOOT_PARAMETERS_GDT 12
+#define TD_BOOT_PARAMETERS_IDT 18
+#define TD_BOOT_PARAMETERS_PER_VCPU 24
+
+/* Offsets for reading struct td_per_vcpu_parameters. */
+#define TD_PER_VCPU_PARAMETERS_ESP_GVA 0
+#define TD_PER_VCPU_PARAMETERS_LJMP_TARGET 4
+
+#define SIZEOF_TD_PER_VCPU_PARAMETERS 10
Please figure out how to replicate the functionality of the kernel's OFFSET()
macro from include/linux/kbuild.h, I have zero desire to maintain open coded
offset values.
