[PATCHv3 2/6] lmb: add LMB_FDT for fdt reserved regions
Ilias Apalodimas
ilias.apalodimas at linaro.org
Thu Apr 16 21:54:13 CEST 2026
On Thu, 16 Apr 2026 at 22:23, Randolph Sapp <rs at ti.com> wrote:
>
> On Thu Apr 16, 2026 at 3:39 AM CDT, Ilias Apalodimas wrote:
> > 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
>
> I did have an initial implementation using a separate allocation list for fdt
> regions in LMB. It works, but boy it's much more messy. All allocations and
> frees had to check both the regular allocation list and the fdt allocation list.
>
> I thought about having the fdt helpers build their own local list separate from
> LMB, but that's also a little messy in that it means we're either double
> tracking regions or tying to reach into the guts of LMB to extract information
> about that existing allocation region.
>
> Maybe that's fine considering LMB already reaches out to kick
> boot_fdt_add_mem_rsv_regions. Just trying to keep things compartmentalized at
> the moment.
>
> I'll revisit the localized reservation list for image-fdt. I'll just setup some
> goofy linked list to track allocation start and size for the later free. I
> assume we prefer a separate set of lmb_region structs for that list as it's a
> little concerning to pass references to an active LMB region outside of the LMB
> core.
Can you explain a bit more when the problem happens? Is it because
boot_fdt_add_mem_rsv_regions() get called twice in some boot flows? Or
is there another reason?
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
> >>
>
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