Messages in this thread | | | Date | Fri, 10 Nov 2017 10:28:12 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH 3/4] x86/boot/compressed/64: Introduce place_trampoline() |
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* Ingo Molnar <mingo@kernel.org> 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 > > One request: it's always going to be fragile if the _only_ thing that uses the > trampoline is the 5-level paging code. > > Could we use the trampoline in the 4-level paging case too? It's not required, but > would test much of the trampoline allocation and copying machinery - and the > performance cost is negligible.
Note that right now the trampoline is pointless on 4-level setups, so there's nothing to copy - but we could perhaps make it meaningful. But maybe it's not a good idea.
One other detail I noticed:
/* Bound size of trampoline code */ .org lvl5_trampoline_src + LVL5_TRAMPOLINE_CODE_SIZE
will this generate a build error if the trampoline code exceeds 0x40?
Thanks,
Ingo
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