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SubjectRe: [PATCH v2 2/2] amr64: map FDT as RW for early_init_dt_scan()
On Mon, May 13, 2019 at 08:38:19AM +0800, Hsin-Yi Wang wrote:
> Currently in arm64, FDT is mapped to RO before it's passed to
> early_init_dt_scan(). However, there might be some code that needs
> to modify FDT during init. Map FDT to RW until unflatten DT.
>
> Signed-off-by: Hsin-Yi Wang <hsinyi@chromium.org>
> ---
> arch/arm64/kernel/setup.c | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
> index 413d566405d1..08b22c1e72a9 100644
> --- a/arch/arm64/kernel/setup.c
> +++ b/arch/arm64/kernel/setup.c
> @@ -179,9 +179,13 @@ static void __init smp_build_mpidr_hash(void)
> pr_warn("Large number of MPIDR hash buckets detected\n");
> }
>
> +extern void *__init __fixmap_remap_fdt(phys_addr_t dt_phys, int *size,
> + pgprot_t prot);
> +
>
> static void __init setup_machine_fdt(phys_addr_t dt_phys)
> {
> - void *dt_virt = fixmap_remap_fdt(dt_phys);
> + int size;
> + void *dt_virt = __fixmap_remap_fdt(dt_phys, &size, PAGE_KERNEL);
> const char *name;

This makes the fdt mapped without the call to meblock_reserve(fdt) which
makes the fdt memory available for memblock allocations.

Chances that is will be actually allocated are small, but you know, things
happen.

IMHO, instead of calling directly __fixmap_remap_fdt() it would be better
to add pgprot parameter to fixmap_remap_fdt(). Then here and in kaslr.c it
can be called with PAGE_KERNEL and below with PAGE_KERNEL_RO.

There is no problem to call memblock_reserve() for the same area twice,
it's essentially a NOP.

> if (!dt_virt || !early_init_dt_scan(dt_virt)) {
> @@ -320,6 +324,9 @@ void __init setup_arch(char **cmdline_p)
> /* Parse the ACPI tables for possible boot-time configuration */
> acpi_boot_table_init();
>
> + /* remap fdt to RO */
> + fixmap_remap_fdt(__fdt_pointer);
> +
> if (acpi_disabled)
> unflatten_device_tree();
>
> --
> 2.20.1
>

--
Sincerely yours,
Mike.

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