[tip:x86/pti] x86/build/64: Force the linker to use 2MB page size

[tip-bot for H.J. Lu]

Commit-ID:  e3d03598e8ae7d195af5d3d049596dec336f569f
Gitweb:     https://git.kernel.org/tip/e3d03598e8ae7d195af5d3d049596dec336f569f
Author:     H.J. Lu <hjl.tools@xxxxxxxxx>
AuthorDate: Mon, 19 Mar 2018 13:57:46 -0700
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Tue, 20 Mar 2018 08:03:03 +0100

x86/build/64: Force the linker to use 2MB page size

Binutils 2.31 will enable -z separate-code by default for x86 to avoid
mixing code pages with data to improve cache performance as well as
security.  To reduce x86-64 executable and shared object sizes, the
maximum page size is reduced from 2MB to 4KB.  But x86-64 kernel must
be aligned to 2MB.  Pass -z max-page-size=0x200000 to linker to force
2MB page size regardless of the default page size used by linker.

Tested with Linux kernel 4.15.6 on x86-64.

Signed-off-by: H.J. Lu <hjl.tools@xxxxxxxxx>
Cc: Andy Shevchenko <andy.shevchenko@xxxxxxxxx>
Cc: Eric Biederman <ebiederm@xxxxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/CAMe9rOp4_%3D_8twdpTyAP2DhONOCeaTOsniJLoppzhoNptL8xzA@xxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 arch/x86/Makefile | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 498c1b812300..1c4d012550ec 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -223,6 +223,15 @@ KBUILD_CFLAGS += $(cfi) $(cfi-sigframe) $(cfi-sections) $(asinstr) $(avx_instr)
 
 LDFLAGS := -m elf_$(UTS_MACHINE)
 
+#
+# The 64-bit kernel must be aligned to 2MB.  Pass -z max-page-size=0x200000 to
+# the linker to force 2MB page size regardless of the default page size used
+# by the linker.
+#
+ifdef CONFIG_X86_64
+LDFLAGS += $(call ld-option, -z max-page-size=0x200000)
+endif
+
 # Speed up the build
 KBUILD_CFLAGS += -pipe
 # Workaround for a gcc prelease that unfortunately was shipped in a suse release