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    Subject[PATCH 5.15 453/846] of/fdt: Dont worry about non-memory region overlap for no-map
    Date
    From: Stephen Boyd <swboyd@chromium.org>

    [ Upstream commit da17d6905d29ddcdc04b2fdc37ed8cf1e8437cc8 ]

    In commit 8a5a75e5e9e5 ("of/fdt: Make sure no-map does not remove
    already reserved regions") we returned -EBUSY when trying to mark
    regions as no-map when they intersect with reserved memory. The goal was
    to find bad no-map reserved memory DT nodes that would unmap the kernel
    text/data sections.

    The problem is the reserved memory check will still trigger if the DT
    has a /memreserve/ that completely subsumes the no-map memory carveouts
    in the reserved memory node _and_ that region is also not part of the
    memory reg property. For example in sc7180.dtsi we have the following
    reserved-memory and memory node:

    memory@80000000 {
    /* We expect the bootloader to fill in the size */
    reg = <0 0x80000000 0 0>;
    };

    smem_mem: memory@80900000 {
    reg = <0x0 0x80900000 0x0 0x200000>;
    no-map;
    };

    and the memreserve filled in by the bootloader is

    /memreserve/ 0x80800000 0x400000;

    while the /memory node is transformed into

    memory@80000000 {
    /* The bootloader fills in the size, and adds another region */
    reg = <0 0x80000000 0 0x00800000>,
    <0 0x80c00000 0 0x7f200000>;
    };

    The smem region is doubly reserved via /memreserve/ and by not being
    part of the /memory reg property. This leads to the following warning
    printed at boot.

    OF: fdt: Reserved memory: failed to reserve memory for node 'memory@80900000': base 0x0000000080900000, size 2 MiB

    Otherwise nothing really goes wrong because the smem region is not going
    to be mapped by the kernel's direct linear mapping given that it isn't
    part of the memory node. Therefore, let's only consider this to be a
    problem if we're trying to mark a region as no-map and it is actually
    memory that we're intending to keep out of the kernel's direct mapping
    but it's already been reserved.

    Acked-by: Mike Rapoport <rppt@kernel.org>
    Cc: Douglas Anderson <dianders@chromium.org>
    Cc: Nicolas Boichat <drinkcat@chromium.org>
    Cc: Quentin Perret <qperret@google.com>
    Cc: Jan Kiszka <jan.kiszka@siemens.com>
    Fixes: 8a5a75e5e9e5 ("of/fdt: Make sure no-map does not remove already reserved regions")
    Signed-off-by: Stephen Boyd <swboyd@chromium.org>
    Signed-off-by: Rob Herring <robh@kernel.org>
    Link: https://lore.kernel.org/r/20220107194233.2793146-1-swboyd@chromium.org
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/of/fdt.c | 6 ++++--
    1 file changed, 4 insertions(+), 2 deletions(-)

    diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
    index 32e5e782d43da..59a7a9ee58ef7 100644
    --- a/drivers/of/fdt.c
    +++ b/drivers/of/fdt.c
    @@ -482,9 +482,11 @@ static int __init early_init_dt_reserve_memory_arch(phys_addr_t base,
    if (nomap) {
    /*
    * If the memory is already reserved (by another region), we
    - * should not allow it to be marked nomap.
    + * should not allow it to be marked nomap, but don't worry
    + * if the region isn't memory as it won't be mapped.
    */
    - if (memblock_is_region_reserved(base, size))
    + if (memblock_overlaps_region(&memblock.memory, base, size) &&
    + memblock_is_region_reserved(base, size))
    return -EBUSY;

    return memblock_mark_nomap(base, size);
    --
    2.34.1


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