[PATCH 4/4] x86: boot: avoid memory copy if kernel is uncompressed

[Albert Huang]

From: "huangjie.albert" <huangjie.albert at bytedance.com>

1、if kernel is uncompressed. we do not need to relocate
kernel image for decompression

2、if kaslr is disabled, we do not need to do a memory copy
before prase_elf.

Two memory copies can be skipped with this patch. this can
save aboat 20ms during booting.

Signed-off-by: huangjie.albert <huangjie.albert at bytedance.com>
---
 arch/x86/boot/compressed/head_64.S |  8 ++++++--
 arch/x86/boot/compressed/misc.c    | 22 +++++++++++++++++-----
 2 files changed, 23 insertions(+), 7 deletions(-)

diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index d33f060900d2..9e7770c7047b 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -398,10 +398,13 @@ SYM_CODE_START(startup_64)
 1:
 
 	/* Target address to relocate to for decompression */
+#ifdef CONFIG_KERNEL_UNCOMPRESSED
+	movq %rbp, %rbx
+#else
 	movl	BP_init_size(%rsi), %ebx
 	subl	$ rva(_end), %ebx
 	addq	%rbp, %rbx
-
+#endif
 	/* Set up the stack */
 	leaq	rva(boot_stack_end)(%rbx), %rsp
 
@@ -522,6 +525,7 @@ trampoline_return:
  * Copy the compressed kernel to the end of our buffer
  * where decompression in place becomes safe.
  */
+#ifndef CONFIG_KERNEL_UNCOMPRESSED
 	pushq	%rsi
 	leaq	(_bss-8)(%rip), %rsi
 	leaq	rva(_bss-8)(%rbx), %rdi
@@ -531,7 +535,7 @@ trampoline_return:
 	rep	movsq
 	cld
 	popq	%rsi
-
+#endif
 	/*
 	 * The GDT may get overwritten either during the copy we just did or
 	 * during extract_kernel below. To avoid any issues, repoint the GDTR
diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
index c23c0f525d93..d8445562d4e9 100644
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -290,7 +290,7 @@ static inline void handle_relocations(void *output, unsigned long output_len,
 { }
 #endif
 
-static void parse_elf(void *output)
+static void parse_elf(void *output, void *input)
 {
 #ifdef CONFIG_X86_64
 	Elf64_Ehdr ehdr;
@@ -302,7 +302,7 @@ static void parse_elf(void *output)
 	void *dest;
 	int i;
 
-	memcpy(&ehdr, output, sizeof(ehdr));
+	memcpy(&ehdr, input, sizeof(ehdr));
 	if (ehdr.e_ident[EI_MAG0] != ELFMAG0 ||
 	   ehdr.e_ident[EI_MAG1] != ELFMAG1 ||
 	   ehdr.e_ident[EI_MAG2] != ELFMAG2 ||
@@ -317,7 +317,7 @@ static void parse_elf(void *output)
 	if (!phdrs)
 		error("Failed to allocate space for phdrs");
 
-	memcpy(phdrs, output + ehdr.e_phoff, sizeof(*phdrs) * ehdr.e_phnum);
+	memcpy(phdrs, input + ehdr.e_phoff, sizeof(*phdrs) * ehdr.e_phnum);
 
 	for (i = 0; i < ehdr.e_phnum; i++) {
 		phdr = &phdrs[i];
@@ -334,7 +334,7 @@ static void parse_elf(void *output)
 #else
 			dest = (void *)(phdr->p_paddr);
 #endif
-			memmove(dest, output + phdr->p_offset, phdr->p_filesz);
+			memmove(dest, input + phdr->p_offset, phdr->p_filesz);
 			break;
 		default: /* Ignore other PT_* */ break;
 		}
@@ -467,9 +467,21 @@ asmlinkage __visible void *extract_kernel(void *rmode, memptr heap,
 #endif
 
 	debug_putstr("\nDecompressing Linux... ");
+
+#ifdef CONFIG_KERNEL_UNCOMPRESSED
+	if (cmdline_find_option_bool("nokaslr")) {
+		parse_elf(output, input_data);
+	} else {
+		__decompress(input_data, input_len, NULL, NULL, output, output_len,
+				NULL, error);
+		parse_elf(output, output);
+	}
+#else
 	__decompress(input_data, input_len, NULL, NULL, output, output_len,
 			NULL, error);
-	parse_elf(output);
+	parse_elf(output, output);
+#endif
+
 	handle_relocations(output, output_len, virt_addr);
 	debug_putstr("done.\nBooting the kernel.\n");
 
-- 
2.31.1