Re: [PATCH 4/4] EFI: free unused boot mem in at least some cases

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 06/08/2020 10:06, Jan Beulich wrote:
> Address at least the primary reason why 52bba67f8b87 ("efi/boot: Don't
> free ebmalloc area at all") was put in place: Make xen_in_range() aware
> of the freed range. This is in particular relevant for EFI-enabled
> builds not actually running on EFI, as the entire range will be unused
> in this case.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> The remaining issue could be addressed too, by making the area 2M in
> size and 2M-aligned.

This memory range is only used for relocating the (synthesized?)
multiboot strings, is it not?

I'm not actually convinced that this is a sensible tradeoff.

For one, you've broken setup.c's:

    /* This needs to remain in sync with xen_in_range(). */
    reserve_e820_ram(&boot_e820, __pa(_stext), __pa(__2M_rwdata_end));

which covers the runtime aspect of what xen_in_range() covers during boot.


I think the better course of action is to go with David Woodhouse's work
to not relocate the trampoline until later on boot (if even necessary),
at which point both of the custom allocators can disappear.

~Andrew