[PATCHv3 2/6] lmb: add LMB_FDT for fdt reserved regions

[Ilias Apalodimas]

Hi Randolph.

On Mon, 13 Apr 2026 at 23:36, <rs at ti.com> wrote:
>
> From: Randolph Sapp <rs at ti.com>
>
> Add an LMB_FDT bit for fdt reserved regions, so we can reclaim them when
> parsing a new device tree and properly warn people when a reservation
> overlaps with an existing allocation.

The LMB has a set of regions that clearly describe memory in an
abstact way, e.g reserved, no overwrite etc.
I don't think adding we should open the door for treating reserved
memory as special. Can't we apply the same fix without adding a new
description?

Thanks
/Ilias
>
> If we don't at least warn the user of these reservation failures,
> there's a chance that this region could be freed and reallocated for
> something important later.
>
> This useful warning mechanism was broken in:
> 5a6aa7d5913 ("boot: fdt: Handle already reserved memory in boot_fdt_reserve_region()")
>
> Signed-off-by: Randolph Sapp <rs at ti.com>
> ---
>  boot/image-fdt.c |  5 ++++-
>  include/lmb.h    | 14 ++++++++++++++
>  lib/lmb.c        | 33 +++++++++++++++++++++++++++++----
>  3 files changed, 47 insertions(+), 5 deletions(-)
>
> diff --git a/boot/image-fdt.c b/boot/image-fdt.c
> index a3a4fb8b558..0f5857f24d2 100644
> --- a/boot/image-fdt.c
> +++ b/boot/image-fdt.c
> @@ -73,6 +73,7 @@ static void boot_fdt_reserve_region(u64 addr, u64 size, u32 flags)
>  {
>         long ret;
>         phys_addr_t rsv_addr;
> +       flags |= LMB_FDT;
>
>         rsv_addr = (phys_addr_t)addr;
>         ret = lmb_alloc_mem(LMB_MEM_ALLOC_ADDR, 0, &rsv_addr, size, flags);
> @@ -80,7 +81,7 @@ static void boot_fdt_reserve_region(u64 addr, u64 size, u32 flags)
>                 debug("   reserving fdt memory region: addr=%llx size=%llx flags=%x\n",
>                       (unsigned long long)addr,
>                       (unsigned long long)size, flags);
> -       } else if (ret != -EEXIST && ret != -EINVAL) {
> +       } else if (ret != -EINVAL) {
>                 puts("ERROR: reserving fdt memory region failed ");
>                 printf("(addr=%llx size=%llx flags=%x)\n",
>                        (unsigned long long)addr,
> @@ -108,6 +109,8 @@ void boot_fdt_add_mem_rsv_regions(void *fdt_blob)
>         if (fdt_check_header(fdt_blob) != 0)
>                 return;
>
> +       lmb_free_fdt_regions();
> +
>         /* process memreserve sections */
>         total = fdt_num_mem_rsv(fdt_blob);
>         for (i = 0; i < total; i++) {
> diff --git a/include/lmb.h b/include/lmb.h
> index 427d701bc30..c6a1fc1ca47 100644
> --- a/include/lmb.h
> +++ b/include/lmb.h
> @@ -51,6 +51,15 @@
>   */
>  #define LMB_NONOTIFY BIT(3)
>
> +/**
> + * define LMB_FDT - reclaim this region with lmb_free_fdt_regions()
> + *
> + * LMB Memory region attribute flag to indicate that the region will be
> + * reclaimed with lmb_free_fdt_regions(). This allows device tree reservations
> + * to be cleaned up and tracked more granularly.
> + */
> +#define LMB_FDT BIT(4)
> +
>  /**
>   * enum lmb_mem_type - type of memory allocation request
>   * @LMB_MEM_ALLOC_ADDR:        request for a particular region of memory
> @@ -235,6 +244,11 @@ phys_addr_t io_lmb_alloc(struct lmb *io_lmb, phys_size_t size, ulong align);
>   */
>  long io_lmb_free(struct lmb *io_lmb, phys_addr_t base, phys_size_t size);
>
> +/**
> + * lmb_free_fdt_regions() - Reclaim all %LMB_FDT tagged reserved regions
> + */
> +void lmb_free_fdt_regions(void);
> +
>  #endif /* __KERNEL__ */
>
>  #endif /* _LINUX_LMB_H */
> diff --git a/lib/lmb.c b/lib/lmb.c
> index 8f12c6ad8e5..7ecc548d831 100644
> --- a/lib/lmb.c
> +++ b/lib/lmb.c
> @@ -463,10 +463,10 @@ static int lmb_map_update_notify(phys_addr_t addr, phys_size_t size,
>
>  static void lmb_print_region_flags(u32 flags)
>  {
> -       const char * const flag_str[] = { "none", "no-map", "no-overwrite",
> -                                         "no-notify" };
> -       unsigned int pflags = flags &
> -                             (LMB_NOMAP | LMB_NOOVERWRITE | LMB_NONOTIFY);
> +       const char *const flag_str[] = { "none", "no-map", "no-overwrite",
> +                                        "no-notify", "fdt" };
> +       unsigned int pflags =
> +               flags & (LMB_NOMAP | LMB_NOOVERWRITE | LMB_NONOTIFY | LMB_FDT);
>
>         if (flags != pflags) {
>                 printf("invalid %#x\n", flags);
> @@ -654,6 +654,31 @@ long lmb_free(phys_addr_t base, phys_size_t size, u32 flags)
>         return lmb_map_update_notify(base, size, LMB_MAP_OP_FREE, flags);
>  }
>
> +void lmb_free_fdt_regions(void)
> +{
> +       struct alist *lmb_rgn_lst = &lmb.used_mem;
> +       struct lmb_region *rgn = lmb_rgn_lst->data;
> +       long ret;
> +       int i = 0;
> +
> +       while (i < lmb_rgn_lst->count) {
> +               phys_addr_t base = rgn[i].base;
> +               phys_size_t size = rgn[i].size;
> +               u32 flags = rgn[i].flags;
> +
> +               if (flags & LMB_FDT) {
> +                       ret = lmb_free(base, size, flags);
> +                       if (ret < 0) {
> +                               printf("Unable to free FDT memory at 0x%08lx\n",
> +                                      (ulong)base);
> +                               i++;
> +                       }
> +               } else {
> +                       i++;
> +               }
> +       }
> +}
> +
>  static int _lmb_alloc_base(phys_size_t size, ulong align,
>                            phys_addr_t *addr, u32 flags)
>  {
> --
> 2.53.0
>