linux-kernel - [RFC PATCH 2/6] x86/boot: Move 5-level paging trampoline into startup code

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Message-ID: <20250401133416.1436741-10-ardb+git@google.com>
Date: Tue,  1 Apr 2025 15:34:19 +0200
From: Ard Biesheuvel <ardb+git@...gle.com>
To: linux-efi@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, x86@...nel.org, 
	Ard Biesheuvel <ardb@...nel.org>, Tom Lendacky <thomas.lendacky@....com>, 
	Dionna Amalie Glaze <dionnaglaze@...gle.com>, Kevin Loughlin <kevinloughlin@...gle.com>
Subject: [RFC PATCH 2/6] x86/boot: Move 5-level paging trampoline into startup code

From: Ard Biesheuvel <ardb@...nel.org>

The 5-level paging trampoline is used by both the EFI stub and the
traditional decompressor. Move it out of the decompressor sources into
the newly minted arch/x86/boot/startup/ sub-directory which will hold
startup code that may be shared between the decompressor, the EFI stub
and the kernel proper, and needs to tolerate being called during early
boot, before the kernel virtual mapping has been created.

This will allow the 5-level paging trampoline to be used by EFI boot
images such as zboot that omit the traditional decompressor entirely.

Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
 arch/x86/Makefile                                  | 1 +
 arch/x86/boot/compressed/Makefile                  | 2 +-
 arch/x86/boot/startup/Makefile                     | 3 +++
 arch/x86/boot/{compressed => startup}/la57toggle.S | 0
 4 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 27efe2dc2aa8..c8703276e3e7 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -287,6 +287,7 @@ archprepare: $(cpufeaturemasks.hdr)
 ###
 # Kernel objects
 
+core-y  += arch/x86/boot/startup/
 libs-y  += arch/x86/lib/
 
 # drivers-y are linked after core-y
diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
index 2eb63536c5d0..468e135de88e 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -98,7 +98,6 @@ ifdef CONFIG_X86_64
 	vmlinux-objs-$(CONFIG_AMD_MEM_ENCRYPT) += $(obj)/mem_encrypt.o
 	vmlinux-objs-y += $(obj)/pgtable_64.o
 	vmlinux-objs-$(CONFIG_AMD_MEM_ENCRYPT) += $(obj)/sev.o
-	vmlinux-objs-y += $(obj)/la57toggle.o
 endif
 
 vmlinux-objs-$(CONFIG_ACPI) += $(obj)/acpi.o
@@ -107,6 +106,7 @@ vmlinux-objs-$(CONFIG_UNACCEPTED_MEMORY) += $(obj)/mem.o
 
 vmlinux-objs-$(CONFIG_EFI) += $(obj)/efi.o
 vmlinux-libs-$(CONFIG_EFI_STUB) += $(objtree)/drivers/firmware/efi/libstub/lib.a
+vmlinux-libs-$(CONFIG_X86_64)	+= $(objtree)/arch/x86/boot/startup/lib.a
 
 $(obj)/vmlinux: $(vmlinux-objs-y) $(vmlinux-libs-y) FORCE
 	$(call if_changed,ld)
diff --git a/arch/x86/boot/startup/Makefile b/arch/x86/boot/startup/Makefile
new file mode 100644
index 000000000000..03519ef4869d
--- /dev/null
+++ b/arch/x86/boot/startup/Makefile
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0
+
+lib-$(CONFIG_X86_64)		+= la57toggle.o
diff --git a/arch/x86/boot/compressed/la57toggle.S b/arch/x86/boot/startup/la57toggle.S
similarity index 100%
rename from arch/x86/boot/compressed/la57toggle.S
rename to arch/x86/boot/startup/la57toggle.S
-- 
2.49.0.472.ge94155a9ec-goog