On Tue, May 14, 2019 at 02:05:43PM -0700, Stephen Boyd wrote:
Quoting Hsin-Yi Wang (2019-05-13 04:14:32)
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?
Why not just have fixmap_remap_fdt() that maps it as RW and reserves memblock once, and then call __fixmap_remap_fdt() with RO after early_init_dt_scan() or unflatten_device_tree() is called? Why the desire to call memblock_reserve() twice or even three times?
There's no desire to call memblock_reserve() twice. It's just that leaving the call for it in kaslr rather than in setup_arch() may end up with unreserved FDT because kaslr was disabled or even compiled out.
I've suggested to use fixmap_remap_fdt() everywhere because IMHO this improves readability and allows to un-export __fixmap_remap_fdt().