* Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> wrote: > --- a/arch/x86/boot/compressed/head_64.S > +++ b/arch/x86/boot/compressed/head_64.S > @@ -315,6 +315,18 @@ ENTRY(startup_64) > * The first step is go into compatibility mode. > */ > > + /* > + * Find suitable place for trampoline and populate it. > + * The address will be stored in RCX. > + * > + * RSI holds real mode data and need to be preserved across > + * a function call. > + */ > + pushq %rsi > + call place_trampoline > + popq %rsi > + movq %rax, %rcx > + > /* Clear additional page table */ > leaq lvl5_pgtable(%rbx), %rdi > xorq %rax, %rax So in the final version of this code we now have: pushq %rsi call need_to_enabled_l5 popq %rsi /* If need_to_enabled_l5() returned zero, we're done here. */ cmpq $0, %rax je lvl5 /* * At this point we are in long mode with 4-level paging enabled, * but we want to enable 5-level paging. * * The problem is that we cannot do it directly. Setting LA57 in * long mode would trigger #GP. So we need to switch off long mode * first. * * We use trampoline in lower memory to handle situation when * bootloader put the kernel image above 4G. * * The first step is go into compatibility mode. */ /* * Find suitable place for trampoline and populate it. * The address will be stored in RCX. * * RSI holds real mode data and need to be preserved across * a function call. */ pushq %rsi call place_trampoline popq %rsi movq %rax, %rcx Firstly, the 'need_to_enabled_l5' name sucks because it includes a typo, but also because the prefix is way too generic. Something like: l5_paging_required() would read a lot better - and would also provide a namespace for all L5 paging related functions. Secondly, couldn't this be combined into a single .c function, named accordingly: l5_paging_prepare() which would return true if L5 paging is available and should be enabled. In this case the trampoline copying function would be called in C, by l5_paging_prepare(). This further reduces the amount of assembly code. Thanks, Ingo -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
