Re: [PATCH v12 08/23] KVM: selftests: Define structs to pass parameters to TDX boot code

Reinette Chatre
2025-10-29T16:37:41Z

Hi Sagi,

On 10/28/25 2:20 PM, Sagi Shahar wrote:
> 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.
>

(sidenote: I do not know what the bar for this work is so I'll defer
comments related to local customs like using "we" and "this patch" in
changelog)

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

> diff --git a/tools/testing/selftests/kvm/Makefile.kvm b/tools/testing/selftests/kvm/Makefile.kvm
> index 148d427ff24b..5e809064ff1c 100644
> --- a/tools/testing/selftests/kvm/Makefile.kvm
> +++ b/tools/testing/selftests/kvm/Makefile.kvm

...

> @@ -328,18 +336,28 @@ $(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__)
> +

Some folks prefer to keep build output separate and may build tests using a command
line like:
make O= TARGETS=kvm -C tools/testing/selftests

This is a valid usage and will result in td_boot_offsets.h placed in that
is not covered by current include path. A build with above command line thus fails:

lib/x86/tdx/td_boot.S:4:10: fatal error: tdx/td_boot_offsets.h: No such file or directory
4 | #include "tdx/td_boot_offsets.h"
| ^~~~~~~~~~~~~~~~~~~~~~~
compilation terminated.

Something like below may be needed to add the output directory to the include path:

diff --git a/tools/testing/selftests/kvm/Makefile.kvm b/tools/testing/selftests/kvm/Makefile.kvm
index 2f49c8965df9..98bc40a7f069 100644
--- a/tools/testing/selftests/kvm/Makefile.kvm
+++ b/tools/testing/selftests/kvm/Makefile.kvm
@@ -262,7 +262,7 @@ CFLAGS += -Wall -Wstrict-prototypes -Wuninitialized -O2 -g -std=gnu99 \
-fno-stack-protector -fno-PIE -fno-strict-aliasing \
-I$(LINUX_TOOL_INCLUDE) -I$(LINUX_TOOL_ARCH_INCLUDE) \
-I$(LINUX_HDR_PATH) -Iinclude -I$(<D) -Iinclude/$(ARCH) \
- -I ../rseq -I.. $(EXTRA_CFLAGS) $(KHDR_INCLUDES)
+ -I ../rseq -I.. -I$(OUTPUT)/include/$(ARCH) $(EXTRA_CFLAGS) $(KHDR_INCLUDES)
ifeq ($(ARCH),s390)
CFLAGS += -march=z10
endif

Reinette