[PATCH 1/5] x86/boot: Initialize boot_params in startup code

Arvind Sankar
2020-10-07T19:54:06Z

Save the boot_params pointer passed in by the bootloader in
startup_32/64. This avoids having to initialize it in two different
places in C code, and having to preserve SI through the early assembly
code.

Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
---
arch/x86/boot/compressed/head_32.S | 11 +++++----
arch/x86/boot/compressed/head_64.S | 34 +++++++++------------------
arch/x86/boot/compressed/misc.c | 10 +-------
arch/x86/boot/compressed/pgtable_64.c | 5 +---
4 files changed, 19 insertions(+), 41 deletions(-)

diff --git a/arch/x86/boot/compressed/head_32.S b/arch/x86/boot/compressed/head_32.S
index 659fad53ca82..c2b014ca92f7 100644
--- a/arch/x86/boot/compressed/head_32.S
+++ b/arch/x86/boot/compressed/head_32.S
@@ -113,6 +113,9 @@ SYM_FUNC_START(startup_32)
addl BP_init_size(%esi), %ebx
subl $_end@GOTOFF, %ebx

+ /* Initialize boot_params */
+ movl %esi, boot_params@GOTOFF(%edx)
+
/* Set up the stack */
leal boot_stack_end@GOTOFF(%ebx), %esp

@@ -124,7 +127,6 @@ SYM_FUNC_START(startup_32)
* Copy the compressed kernel to the end of our buffer
* where decompression in place becomes safe.
*/
- pushl %esi
leal (_bss@GOTOFF-4)(%edx), %esi
leal (_bss@GOTOFF-4)(%ebx), %edi
movl $(_bss - startup_32), %ecx
@@ -132,7 +134,6 @@ SYM_FUNC_START(startup_32)
std
rep movsl
cld
- popl %esi

/*
* The GDT may get overwritten either during the copy we just did or
@@ -187,14 +188,12 @@ SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated)
pushl %eax /* input_data */
leal boot_heap@GOTOFF(%ebx), %eax
pushl %eax /* heap area */
- pushl %esi /* real mode pointer */
call extract_kernel /* returns kernel location in %eax */
- addl $24, %esp

/*
* Jump to the extracted kernel.
*/
- xorl %ebx, %ebx
+ movl boot_params@GOTOFF(%ebx), %esi
jmp *%eax
SYM_FUNC_END(.Lrelocated)

@@ -209,6 +208,8 @@ SYM_DATA_START_LOCAL(gdt)
.quad 0x00cf92000000ffff /* __KERNEL_DS */
SYM_DATA_END_LABEL(gdt, SYM_L_LOCAL, gdt_end)

+SYM_DATA(boot_params, .long 0)
+
#ifdef CONFIG_EFI_STUB
SYM_DATA(image_offset, .long 0)
#endif
diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index 1c80f1738fd9..78f873f76579 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -375,6 +375,9 @@ SYM_CODE_START(startup_64)
subl $ rva(_end), %ebx
addq %rbp, %rbx

+ /* Initialize boot_params */
+ movq %rsi, boot_params(%rip)
+
/* Set up the stack */
leaq rva(boot_stack_end)(%rbx), %rsp

@@ -429,14 +432,8 @@ SYM_CODE_START(startup_64)
* - Address of the trampoline is returned in RAX.
* - Non zero RDX means trampoline needs to enable 5-level
* paging.
- *
- * RSI holds real mode data and needs to be preserved across
- * this function call.
*/
- pushq %rsi
- movq %rsi, %rdi /* real mode address */
call paging_prepare
- popq %rsi

/* Save the trampoline address in RCX */
movq %rax, %rcx
@@ -461,14 +458,9 @@ trampoline_return:
*
* RDI is address of the page table to use instead of page table
* in trampoline memory (if required).
- *
- * RSI holds real mode data and needs to be preserved across
- * this function call.
*/
- pushq %rsi
leaq rva(top_pgtable)(%rbx), %rdi
call cleanup_trampoline
- popq %rsi

/* Zero EFLAGS */
pushq $0
@@ -478,7 +470,6 @@ trampoline_return:
* Copy the compressed kernel to the end of our buffer
* where decompression in place becomes safe.
*/
- pushq %rsi
leaq (_bss-8)(%rip), %rsi
leaq rva(_bss-8)(%rbx), %rdi
movl $(_bss - startup_32), %ecx
@@ -486,7 +477,6 @@ trampoline_return:
std
rep movsq
cld
- popq %rsi

/*
* The GDT may get overwritten either during the copy we just did or
@@ -541,28 +531,24 @@ SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated)
* handler. Then load stage2 IDT and switch to the kernel's own
* page-table.
*/
- pushq %rsi
call set_sev_encryption_mask
call load_stage2_idt
call initialize_identity_maps
- popq %rsi

/*
* Do the extraction, and jump to the new kernel..
*/
- pushq %rsi /* Save the real mode argument */
- movq %rsi, %rdi /* real mode address */
- leaq boot_heap(%rip), %rsi /* malloc area for uncompression */
- leaq input_data(%rip), %rdx /* input_data */
- movl input_len(%rip), %ecx /* input_len */
- movq %rbp, %r8 /* output target address */
- movl output_len(%rip), %r9d /* decompressed length, end of relocs */
+ leaq boot_heap(%rip), %rdi /* malloc area for uncompression */
+ leaq input_data(%rip), %rsi /* input_data */
+ movl input_len(%rip), %edx /* input_len */
+ movq %rbp, %rcx /* output target address */
+ movl output_len(%rip), %r8d /* decompressed length, end of relocs */
call extract_kernel /* returns kernel location in %rax */
- popq %rsi

/*
* Jump to the decompressed kernel.
*/
+ movq boot_params(%rip), %rsi
jmp *%rax
SYM_FUNC_END(.Lrelocated)

@@ -691,6 +677,8 @@ SYM_DATA_START(boot_idt)
.endr
SYM_DATA_END_LABEL(boot_idt, SYM_L_GLOBAL, boot_idt_end)

+SYM_DATA(boot_params, .quad 0)
+
#ifdef CONFIG_EFI_STUB
SYM_DATA(image_offset, .long 0)
#endif
diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
index 267e7f93050e..279631650bd8 100644
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -39,11 +39,6 @@
/* Functions used by the included decompressor code below. */
void *memmove(void *dest, const void *src, size_t n);

-/*
- * This is set up by the setup-routine at boot-time
- */
-struct boot_params *boot_params;
-
memptr free_mem_ptr;
memptr free_mem_end_ptr;

@@ -338,7 +333,7 @@ static void parse_elf(void *output)
* |-------uncompressed kernel image---------|
*
*/
-asmlinkage __visible void *extract_kernel(void *rmode, memptr heap,
+asmlinkage __visible void *extract_kernel(memptr heap,
unsigned char *input_data,
unsigned long input_len,
unsigned char *output,
@@ -348,9 +343,6 @@ asmlinkage __visible void *extract_kernel(void *rmode, memptr heap,
unsigned long virt_addr = LOAD_PHYSICAL_ADDR;
unsigned long needed_size;

- /* Retain x86 boot parameters pointer passed from startup_32/64. */
- boot_params = rmode;
-
/* Clear flags intended for solely in-kernel use. */
boot_params->hdr.loadflags &= ~KASLR_FLAG;

diff --git a/arch/x86/boot/compressed/pgtable_64.c b/arch/x86/boot/compressed/pgtable_64.c
index 7d0394f4ebf9..0fb948c0c8b4 100644
--- a/arch/x86/boot/compressed/pgtable_64.c
+++ b/arch/x86/boot/compressed/pgtable_64.c
@@ -98,13 +98,10 @@ static unsigned long find_trampoline_placement(void)
return bios_start - TRAMPOLINE_32BIT_SIZE;
}

-struct paging_config paging_prepare(void *rmode)
+struct paging_config paging_prepare(void)
{
struct paging_config paging_config = {};

- /* Initialize boot_params. Required for cmdline_find_option_bool(). */
- boot_params = rmode;
-
/*
* Check if LA57 is desired and supported.
*
--
2.26.2