Instead of pushing and popping %RSI several times to preserve the struct boot_params pointer across the execution of the startup code, move it into a callee save register before the first call into C, and copy it back when needed. Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx> --- arch/x86/boot/compressed/head_64.S | 38 +++++++------------- 1 file changed, 13 insertions(+), 25 deletions(-) diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S index b1367f34e2881fc7..2ccddec2220ce914 100644 --- a/arch/x86/boot/compressed/head_64.S +++ b/arch/x86/boot/compressed/head_64.S @@ -405,10 +405,14 @@ SYM_CODE_START(startup_64) lretq .Lon_kernel_cs: + /* + * RSI holds a pointer to a boot_params structure provided by the + * loader, and this needs to be preserved across C function calls. So + * move it into a callee saved register. + */ + movq %rsi, %r15 - pushq %rsi call load_stage1_idt - popq %rsi #ifdef CONFIG_AMD_MEM_ENCRYPT /* @@ -421,10 +425,8 @@ SYM_CODE_START(startup_64) * detection/setup to ensure that has been done in advance of any dependent * code. */ - pushq %rsi - movq %rsi, %rdi /* real mode address */ + movq %r15, %rdi /* pass struct boot_params pointer */ call sev_enable - popq %rsi #endif /* @@ -437,13 +439,9 @@ SYM_CODE_START(startup_64) * - 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 */ + movq %r15, %rdi /* pass struct boot_params pointer */ call paging_prepare - popq %rsi /* Save the trampoline address in RCX */ movq %rax, %rcx @@ -461,9 +459,9 @@ SYM_CODE_START(startup_64) pushq %rdi /* Preserve other live 64-bit registers */ + pushq %r15 pushq %rbp pushq %rbx - pushq %rsi /* Switch to compatibility mode (CS.L = 0 CS.D = 1) via far return */ pushq $__KERNEL32_CS @@ -479,14 +477,9 @@ 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 @@ -496,7 +489,6 @@ 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 @@ -504,7 +496,6 @@ trampoline_return: std rep movsq cld - popq %rsi /* * The GDT may get overwritten either during the copy we just did or @@ -536,30 +527,27 @@ SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated) shrq $3, %rcx rep stosq - pushq %rsi call load_stage2_idt /* Pass boot_params to initialize_identity_maps() */ - movq (%rsp), %rdi + movq %r15, %rdi /* pass struct boot_params pointer */ 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 */ + movq %r15, %rdi /* pass struct boot_params pointer */ 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 */ call extract_kernel /* returns kernel entry point in %rax */ - popq %rsi /* * Jump to the decompressed kernel. */ + movq %r15, %rsi jmp *%rax SYM_FUNC_END(.Lrelocated) @@ -653,9 +641,9 @@ SYM_CODE_END(trampoline_32bit_src) .code64 SYM_FUNC_START_LOCAL_NOALIGN(.Lpaging_enabled) /* Return from the trampoline */ - popq %rsi popq %rbx popq %rbp + popq %r15 retq SYM_FUNC_END(.Lpaging_enabled) -- 2.39.2
