Re: [PATCH 21/26] x86/mm: add support of additional page table level during early boot

[Kirill A. Shutemov]

On Wed, Apr 05, 2017 at 02:36:24PM +0300, Kirill A. Shutemov wrote:
> On Mon, Mar 13, 2017 at 08:18:10AM +0100, Ingo Molnar wrote:
> > 
> > * Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> wrote:
> > 
> > > This patch adds support for 5-level paging during early boot.
> > > It generalizes boot for 4- and 5-level paging on 64-bit systems with
> > > compile-time switch between them.
> > > 
> > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> > > ---
> > >  arch/x86/boot/compressed/head_64.S          | 23 +++++++++--
> > >  arch/x86/include/asm/pgtable.h              |  2 +-
> > >  arch/x86/include/asm/pgtable_64.h           |  6 ++-
> > >  arch/x86/include/uapi/asm/processor-flags.h |  2 +
> > >  arch/x86/kernel/espfix_64.c                 |  2 +-
> > >  arch/x86/kernel/head64.c                    | 40 +++++++++++++-----
> > >  arch/x86/kernel/head_64.S                   | 63 +++++++++++++++++++++--------
> > 
> > Ok, here I'd like to have a C version instead of further complicating an already 
> > complex assembly version...
> 
> Just head up: I work on this.
> 
> It's great deal of frustration (I can't really read assembly), but I'm
> slowly moving forward.
> 
> Most of logic in startup_64 in arch/x86/kernel/head_64.S is converted
> to C. Dealing with secondary_startup_64 now.

I'm stuck with secondary_startup_64 too. Stack breaks as soon as we switch
to new page tables when onlining secondary CPUs. I don't know how to get
around this.

Would it be sufficient if I only convert startup_64 in
arch/x86/kernel/head_64.S to C?

-- 
 Kirill A. Shutemov