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

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Message-ID: <d4813147-920e-40a4-a7f7-e93666c77cc1@intel.com>
Date: Wed, 29 Oct 2025 09:37:29 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Sagi Shahar <sagis@...gle.com>, <linux-kselftest@...r.kernel.org>, "Paolo
 Bonzini" <pbonzini@...hat.com>, Shuah Khan <shuah@...nel.org>, "Sean
 Christopherson" <seanjc@...gle.com>, Ackerley Tng <ackerleytng@...gle.com>,
	Ryan Afranji <afranji@...gle.com>, Andrew Jones <ajones@...tanamicro.com>,
	Isaku Yamahata <isaku.yamahata@...el.com>, Erdem Aktas
	<erdemaktas@...gle.com>, Rick Edgecombe <rick.p.edgecombe@...el.com>, "Roger
 Wang" <runanwang@...gle.com>, Binbin Wu <binbin.wu@...ux.intel.com>, "Oliver
 Upton" <oliver.upton@...ux.dev>, "Pratik R. Sampat"
	<pratikrajesh.sampat@....com>, Ira Weiny <ira.weiny@...el.com>, Chao Gao
	<chao.gao@...el.com>, Chenyi Qiang <chenyi.qiang@...el.com>
CC: <linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>
Subject: Re: [PATCH v12 08/23] KVM: selftests: Define structs to pass
 parameters to TDX boot code

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=<output dir> TARGETS=kvm -C tools/testing/selftests

This is a valid usage and will result in td_boot_offsets.h placed in <output dir> 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