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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 4:59 PM Mike Rapoport <rppt@linux.ibm.com> wrote:

>
> 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.
>
Thanks for the suggestion. Will update fixmap_remap_fdt() in next patch.

However, I tested on some arm64 platform, if we also call
memblock_reserve() in kaslr.c, would cause warning[1] when
memblock_reserve() is called again in setup_machine_fdt(). The warning
comes from https://elixir.bootlin.com/linux/latest/source/mm/memblock.c#L601
```
if (type->regions[0].size == 0) {
WARN_ON(type->cnt != 1 || type->total_size);
...
```

Call memblock_reserve() multiple times after setup_machine_fdt()
doesn't have such warning though.

I didn't trace the real reason causing this. But in this case, maybe
don't call memblock_reserve() in kaslr?

[1]
[ 0.000000] WARNING: CPU: 0 PID: 0 at
/mnt/host/source/src/third_party/kernel/v4.19/mm/memblock.c:583
memblock_add_range+0x1bc/0x1c8
[ 0.000000] Modules linked in:
[ 0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 4.19.38 #125
[ 0.000000] pstate: 600001c5 (nZCv dAIF -PAN -UAO)
[ 0.000000] pc : memblock_add_range+0x1bc/0x1c8
[ 0.000000] lr : memblock_add_range+0x30/0x1c8
[ 0.000000] sp : ffffff9b5e203e80
[ 0.000000] x29: ffffff9b5e203ed0 x28: 0000000040959324
[ 0.000000] x27: 0000000040080000 x26: 0000000000080000
[ 0.000000] x25: 0000000080127e4b x24: 0000000000000000
[ 0.000000] x23: 0000001b55000000 x22: 000000000001152b
[ 0.000000] x21: 000000005f800000 x20: 0000000000000000
[ 0.000000] x19: ffffff9b5e24bf00 x18: 00000000ffffffb8
[ 0.000000] x17: 000000000000003c x16: ffffffbefea00000
[ 0.000000] x15: ffffffbefea00000 x14: ffffff9b5e3c17d8
[ 0.000000] x13: 00e8000000000713 x12: 0000000000000000
[ 0.000000] x11: ffffffbefea00000 x10: 00e800005f800710
[ 0.000000] x9 : 000000000001152b x8 : ffffff9b5e365690
[ 0.000000] x7 : 6f20646573616228 x6 : 0000000000000002
[ 0.000000] x5 : 0000000000000000 x4 : 0000000000000000
[ 0.000000] x3 : 0000000000200000 x2 : 000000000001152b
[ 0.000000] x1 : 000000005f800000 x0 : ffffff9b5e24bf00
[ 0.000000] Call trace:
[ 0.000000] memblock_add_range+0x1bc/0x1c8
[ 0.000000] memblock_reserve+0x60/0xac
[ 0.000000] fixmap_remap_fdt+0x4c/0x78
[ 0.000000] setup_machine_fdt+0x64/0xfc
[ 0.000000] setup_arch+0x68/0x1e0
[ 0.000000] start_kernel+0x68/0x380

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