Re: [PATCH v2] xen/arm/efi: merge neighboring banks

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Thu, 27 Mar 2025, Volodymyr Babchuk wrote:
> Hi Stefano,
> 
> Stefano Stabellini <stefano.stabellini@xxxxxxx> writes:
> 
> > When booting from U-Boot bootefi, there can be a high number of
> > neighboring RAM banks. See for example:
> >
> > (XEN) RAM: 0000000000000000 - 0000000000bfffff
> > (XEN) RAM: 0000000000c00000 - 0000000000c00fff
> > (XEN) RAM: 0000000000c01000 - 0000000000dfffff
> > (XEN) RAM: 0000000000e00000 - 000000000279dfff
> > (XEN) RAM: 000000000279e000 - 00000000029fffff
> > (XEN) RAM: 0000000002a00000 - 0000000008379fff
> > (XEN) RAM: 000000000837a000 - 00000000083fffff
> > (XEN) RAM: 0000000008400000 - 0000000008518fff
> > (XEN) RAM: 0000000008519000 - 00000000085fffff
> > (XEN) RAM: 0000000008600000 - 0000000008613fff
> > (XEN) RAM: 0000000008614000 - 00000000097fffff
> > (XEN) RAM: 0000000009800000 - 00000000098a7fff
> > (XEN) RAM: 00000000098a8000 - 0000000009dfffff
> > (XEN) RAM: 0000000009e00000 - 0000000009ea7fff
> > (XEN) RAM: 0000000009ea8000 - 000000001fffffff
> > (XEN) RAM: 0000000020000000 - 000000002007ffff
> > (XEN) RAM: 0000000020080000 - 0000000077b17fff
> > (XEN) RAM: 0000000077b19000 - 0000000077b2bfff
> > (XEN) RAM: 0000000077b2c000 - 0000000077c8dfff
> > (XEN) RAM: 0000000077c8e000 - 0000000077c91fff
> > (XEN) RAM: 0000000077ca7000 - 0000000077caafff
> > (XEN) RAM: 0000000077cac000 - 0000000077caefff
> > (XEN) RAM: 0000000077cd0000 - 0000000077cd2fff
> > (XEN) RAM: 0000000077cd4000 - 0000000077cd7fff
> > (XEN) RAM: 0000000077cd8000 - 000000007bd07fff
> > (XEN) RAM: 000000007bd09000 - 000000007fd5ffff
> > (XEN) RAM: 000000007fd70000 - 000000007fefffff
> > (XEN) RAM: 0000000800000000 - 000000087fffffff
> >
> > Xen does not currently support boot modules that span multiple banks: at
> > least one of the regions get freed twice. The first time from
> > setup_mm->populate_boot_allocator, then again from
> > discard_initial_modules->fw_unreserved_regions. With a high number of
> > banks, it can be difficult to arrange the boot modules in a way that
> > avoids spanning across multiple banks.
> >
> > This small patch merges neighboring regions, to make dealing with them
> > more efficient, and to make it easier to load boot modules.
> >
> > Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxx>
> > ---
> > Changes in v2:
> > - remove unneeded check for duplicates
> > - unsigned int instead of int
> > - add parenthesis
> > ---
> >  xen/arch/arm/efi/efi-boot.h | 10 ++++++++++
> >  1 file changed, 10 insertions(+)
> >
> > diff --git a/xen/arch/arm/efi/efi-boot.h b/xen/arch/arm/efi/efi-boot.h
> > index a80a5a7ab3..8b8ef5dcfb 100644
> > --- a/xen/arch/arm/efi/efi-boot.h
> > +++ b/xen/arch/arm/efi/efi-boot.h
> > @@ -163,6 +163,16 @@ static bool __init meminfo_add_bank(struct membanks 
> > *mem,
> >      struct membank *bank;
> >      paddr_t start = desc->PhysicalStart;
> >      paddr_t size = desc->NumberOfPages * EFI_PAGE_SIZE;
> > +    unsigned int j;
> > +
> > +    for ( j = 0; j < mem->nr_banks; j++ )
> > +    {
> > +        if ( (mem->bank[j].start + mem->bank[j].size) == start )
> > +        {
> > +            mem->bank[j].size += size;
> > +            return true;
> > +        }
> > +    }
> >  
> >      if ( mem->nr_banks >= mem->max_banks )
> >          return false;
> 
> It didn't got into diff context, but there is this check below:
> 
> #ifdef CONFIG_ACPI
>     if ( check_reserved_regions_overlap(start, size, false) )
>         return false;
> #endif
> 
> Your patch will skip it.

You are right, this new hunk should be added after that check. I'l
resend.