[PATCH 5/6] efi_memory: backfill EFI_CONVENTIONAL_MEMORY

[Ilias Apalodimas]

Hi Randolph

On Thu, 2 Apr 2026 at 03:14, <rs at ti.com> wrote:
>
> From: Randolph Sapp <rs at ti.com>
>
> Backfill any fragmented EFI_CONVENTIONAL_MEMORY when LMB allocations
> start to fail. This may be a low memory environment, or maybe LMB is
> running up against a tricky reserved region.
>
> Signed-off-by: Randolph Sapp <rs at ti.com>
> ---
>  lib/efi_loader/efi_memory.c | 35 +++++++++++++++++++++++++++++++++--
>  1 file changed, 33 insertions(+), 2 deletions(-)
>
> diff --git a/lib/efi_loader/efi_memory.c b/lib/efi_loader/efi_memory.c
> index 882366a9f8a..f07cc39b157 100644
> --- a/lib/efi_loader/efi_memory.c
> +++ b/lib/efi_loader/efi_memory.c
> @@ -441,6 +441,27 @@ static efi_status_t efi_check_allocated(u64 addr, bool must_be_allocated)
>         return EFI_NOT_FOUND;
>  }
>
> +/**
> + * efi_get_conventional_start - find the highest conventional region start
> + *                              address with at least the specified number of
> + *                              pages
> + *
> + * @pages:                      number of pages required to be in that carveout
> + * Return:                      starting address of the give carveout
> + */
> +static u64 efi_get_conventional_start(u64 pages)
> +{
> +       struct efi_mem_list *item;
> +
> +       list_for_each_entry(item, &efi_mem, link) {
> +               if (item->desc.type != EFI_CONVENTIONAL_MEMORY)
> +                       continue;
> +               if (item->desc.num_pages >= pages)
> +                       return item->desc.physical_start;
> +       }
> +       return 0;

We've been bitten by this in the past and although unlikely 0 is a
valid address for some hardware. Can we return something different if
we don't find a match? UINT64_MAX perhaps?

> +}
> +
>  /**
>   * efi_allocate_pages - allocate memory pages
>   *
> @@ -507,10 +528,20 @@ efi_status_t efi_allocate_pages(enum efi_allocate_type type,
>         /* Reserve that map in our memory maps */
>         ret = efi_update_memory_map(efi_addr, pages, memory_type, true, false);

In theory the lmb and the EFI maps are in sync. I haven't checked
close enough yet, but do you have cases where lmb_alloc worked and
updating the efi memory map failed?

>         if (ret != EFI_SUCCESS) {
> -               /* Map would overlap, bail out */
> +               /* Map would overlap, try something else */
>                 lmb_free(addr, (u64)pages << EFI_PAGE_SHIFT, flags);
>                 unmap_sysmem((void *)(uintptr_t)efi_addr);
> -               return  EFI_OUT_OF_RESOURCES;
> +
> +               /* See if there is any EFI_CONVENTIONAL_MEMORY allocations */
> +               if (type != EFI_ALLOCATE_ADDRESS) {

Can you please inverse this. It's going to reduce the identation.
if (type == EFI_ALLOCATE_ADDRESS)
> +                       *memory = efi_get_conventional_start(pages);
> +                       if (*memory != 0)

Same here

> +                               return efi_allocate_pages(EFI_ALLOCATE_ADDRESS,
> +                                                         memory_type, pages,
> +                                                         memory);
> +               }
> +
> +               return EFI_OUT_OF_RESOURCES;
>         }
>
>         *memory = efi_addr;
> --
> 2.53.0
>

Thanks
/Ilias