linux-kernel - [PATCH 20/21] x86/power: Move restore

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Date:   Thu, 14 Jan 2021 13:40:16 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        clang-built-linux@...glegroups.com,
        Miroslav Benes <mbenes@...e.cz>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Pavel Machek <pavel@....cz>
Subject: [PATCH 20/21] x86/power: Move restore_registers() to top of the file

Because restore_registers() is page-aligned, the assembler inexplicably
adds an unreachable jump from after the end of the previous function to
the beginning of restore_registers().

That confuses objtool, understandably.  It also creates significant text
fragmentation.  As a result, most of the object file is wasted text
(nops).

Move restore_registers() to the beginning of the file to both prevent
the text fragmentation and avoid the dead jump instruction.

$ size /tmp/hibernate_asm_64.before.o /tmp/hibernate_asm_64.after.o
   text	   data	    bss	    dec	    hex	filename
   4415	      0	      0	   4415	   113f	/tmp/hibernate_asm_64.before.o
    524	      0	      0	    524	    20c	/tmp/hibernate_asm_64.after.o

Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc: Pavel Machek <pavel@....cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
---
 arch/x86/power/hibernate_asm_64.S | 92 +++++++++++++++----------------
 1 file changed, 46 insertions(+), 46 deletions(-)

diff --git a/arch/x86/power/hibernate_asm_64.S b/arch/x86/power/hibernate_asm_64.S
index 24d971911c9d..4ca6d68b0293 100644
--- a/arch/x86/power/hibernate_asm_64.S
+++ b/arch/x86/power/hibernate_asm_64.S
@@ -23,6 +23,52 @@
 #include <asm/frame.h>
 #include <asm/nospec-branch.h>
 
+	 /* code below belongs to the image kernel */
+	.align PAGE_SIZE
+SYM_FUNC_START(restore_registers)
+	/* go back to the original page tables */
+	movq    %r9, %cr3
+
+	/* Flush TLB, including "global" things (vmalloc) */
+	movq	mmu_cr4_features(%rip), %rax
+	movq	%rax, %rdx
+	andq	$~(X86_CR4_PGE), %rdx
+	movq	%rdx, %cr4;  # turn off PGE
+	movq	%cr3, %rcx;  # flush TLB
+	movq	%rcx, %cr3
+	movq	%rax, %cr4;  # turn PGE back on
+
+	/* We don't restore %rax, it must be 0 anyway */
+	movq	$saved_context, %rax
+	movq	pt_regs_sp(%rax), %rsp
+	movq	pt_regs_bp(%rax), %rbp
+	movq	pt_regs_si(%rax), %rsi
+	movq	pt_regs_di(%rax), %rdi
+	movq	pt_regs_bx(%rax), %rbx
+	movq	pt_regs_cx(%rax), %rcx
+	movq	pt_regs_dx(%rax), %rdx
+	movq	pt_regs_r8(%rax), %r8
+	movq	pt_regs_r9(%rax), %r9
+	movq	pt_regs_r10(%rax), %r10
+	movq	pt_regs_r11(%rax), %r11
+	movq	pt_regs_r12(%rax), %r12
+	movq	pt_regs_r13(%rax), %r13
+	movq	pt_regs_r14(%rax), %r14
+	movq	pt_regs_r15(%rax), %r15
+	pushq	pt_regs_flags(%rax)
+	popfq
+
+	/* Saved in save_processor_state. */
+	lgdt	saved_context_gdt_desc(%rax)
+
+	xorl	%eax, %eax
+
+	/* tell the hibernation core that we've just restored the memory */
+	movq	%rax, in_suspend(%rip)
+
+	ret
+SYM_FUNC_END(restore_registers)
+
 SYM_FUNC_START(swsusp_arch_suspend)
 	movq	$saved_context, %rax
 	movq	%rsp, pt_regs_sp(%rax)
@@ -100,49 +146,3 @@ SYM_CODE_START(core_restore_code)
 	/* jump to the restore_registers address from the image header */
 	JMP_NOSPEC r8
 SYM_CODE_END(core_restore_code)
-
-	 /* code below belongs to the image kernel */
-	.align PAGE_SIZE
-SYM_FUNC_START(restore_registers)
-	/* go back to the original page tables */
-	movq    %r9, %cr3
-
-	/* Flush TLB, including "global" things (vmalloc) */
-	movq	mmu_cr4_features(%rip), %rax
-	movq	%rax, %rdx
-	andq	$~(X86_CR4_PGE), %rdx
-	movq	%rdx, %cr4;  # turn off PGE
-	movq	%cr3, %rcx;  # flush TLB
-	movq	%rcx, %cr3
-	movq	%rax, %cr4;  # turn PGE back on
-
-	/* We don't restore %rax, it must be 0 anyway */
-	movq	$saved_context, %rax
-	movq	pt_regs_sp(%rax), %rsp
-	movq	pt_regs_bp(%rax), %rbp
-	movq	pt_regs_si(%rax), %rsi
-	movq	pt_regs_di(%rax), %rdi
-	movq	pt_regs_bx(%rax), %rbx
-	movq	pt_regs_cx(%rax), %rcx
-	movq	pt_regs_dx(%rax), %rdx
-	movq	pt_regs_r8(%rax), %r8
-	movq	pt_regs_r9(%rax), %r9
-	movq	pt_regs_r10(%rax), %r10
-	movq	pt_regs_r11(%rax), %r11
-	movq	pt_regs_r12(%rax), %r12
-	movq	pt_regs_r13(%rax), %r13
-	movq	pt_regs_r14(%rax), %r14
-	movq	pt_regs_r15(%rax), %r15
-	pushq	pt_regs_flags(%rax)
-	popfq
-
-	/* Saved in save_processor_state. */
-	lgdt	saved_context_gdt_desc(%rax)
-
-	xorl	%eax, %eax
-
-	/* tell the hibernation core that we've just restored the memory */
-	movq	%rax, in_suspend(%rip)
-
-	ret
-SYM_FUNC_END(restore_registers)
-- 
2.29.2