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    SubjectRe: [PATCH] riscv: reserve DTB before possible memblock allocation
    On Thu, Jun 08, 2023 at 09:49:44AM +0200, Alexandre Ghiti wrote:
    > On Wed, Jun 7, 2023 at 8:17 PM Conor Dooley <conor@kernel.org> wrote:
    > >
    > > +CC Alex, you should take a look at this patch.
    > >
    > > On Wed, Jun 07, 2023 at 09:35:19PM +0800, Woody Zhang wrote:
    > > > It's possible that early_init_fdt_scan_reserved_mem() allocates memory
    > > > from memblock for dynamic reserved memory in `/reserved-memory` node.
    > > > Any fixed reservation must be done before that to avoid potential
    > > > conflicts.
    > > >
    > > > Reserve the DTB in memblock just after early scanning it.
    > >
    > > The rationale makes sense to me, I am just wondering what compelling
    > > reason there is to move it away from the memblock_reserve()s for the
    > > initd and vmlinux? Moving it above early_init_fdt_scan_reserved_mem()
    > > should be the sufficient minimum & would keep things together.

    > Thanks Conor.
    >
    > So the patch looks good to me.
    >
    > But I find this fragile:
    >
    > - we do not check memblock_reserve() return value to make sure the
    > reservation really happened (and quickly looking at the code, I'm not
    > even sure it returns an error if the region was already allocated).
    > - we have to make sure no memblock allocation happens before setup_bootmem().
    > - we also have to check that no fixed memblock_reserve() happens after.
    >
    > The last 2 points may sound natural, but we'll have to take great care
    > when adding some code around here. I'm working on an "early boot
    > document" and I'll add something about that, but a runtime thing would
    > be way better IMO.
    >
    > You can add:
    >
    > Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>

    btw Alex/Woody, what is the appropriate Fixes tag here?

    Cheers,
    Conor.
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