Re: [Xen-devel] [PATCH v6 08/15] x86/efi: create new early memory allocator

[Daniel Kiper <daniel.kiper@xxxxxxxxxx>]

On Fri, Sep 23, 2016 at 12:07:14PM +0100, Julien Grall wrote:
> On 23/09/16 11:50, Daniel Kiper wrote:
> >Hi Julien,
>
> Hi Daniel,
>
> >
> >On Thu, Sep 22, 2016 at 06:07:26PM +0100, Julien Grall wrote:
> >
> >[...]
> >
> >>>#ifndef CONFIG_ARM
> >>>/* Whole x86 ebmalloc stuff. */
> >>>...
> >>>#else
> >>>void __init free_ebmalloc_unused_mem(void)
> >>>{
> >>>}
> >>>#endif
> >>>
> >>>and then call free_ebmalloc_unused_mem() from e.g.
> >>>xen/arch/arm/setup.c:init_done(). Am I right?
> >>
> >>Bear in mind that the EFI loader on ARM is standalone. It cannot
> >>interact with Xen.
> >>
> >>The main goal of the EFI stub is to load the different images on the
> >>memory and then will jump at the same starting point as when Xen is
> >>loaded without EFI. So anything in bss will be zeroed.
> >
> >AIUI, on ARM EFI we have following call sequence:
> >  - efi_start(),
> >  - efi_xen_start(),
> >  - real_start()
> >  - ...
> >  - el2() which zeroes BSS... ;-(((
> >
> >We had the same situation on x86. So, we moved BSS init just before
> >efi_start() call and disabled later zero BSS if we are booted via EFI.
> >Could we do the same on ARM? As I can see Jan wish to use ebmalloc on
> >ARM too. Does it make sense for you?
>
> The EFI on ARM has been designed to be standalone and disable page
> tables, flush the cache before hand and then jump in the startup
> beginning of the binary (as it would be done without EFI).
>
> The problem I can see here, is ebmalloc_mem is allocated in bss
> rather than in init. I understand this is an optimization, to shrink
> down the size of the binary.
>
> But, I am not in favor to start differing in startup code if we have
> EFI enabled just for that.
>
> IHMO, anything related to the stub should be in the init section and
> therefore will be freed when Xen has finished to boot.

One early allocator for both platforms would be nice. And I have a feeling
that this is the Jan's goal. However, I am not going to insist because you
know ARM platforms better than I. So, I think that Jan should say what is
his idea in this situation.

Daniel

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