Hello Christophe,
On Tue, Feb 20, 2018 at 06:45:09PM +0100, christophe leroy wrote:
[...]
> > - if (slab_is_available() && (p < virt_to_phys(high_memory)) &&
> > + if (slab_is_available() && pfn_valid(__phys_to_pfn(p)) &&
>
> I'm not sure this is equivalent:
>
> high_memory = (void *) __va(max_low_pfn * PAGE_SIZE);
> #define ARCH_PFN_OFFSET ((unsigned long)(MEMORY_START >> PAGE_SHIFT))
> #define pfn_valid(pfn) ((pfn) >= ARCH_PFN_OFFSET && (pfn) < max_mapnr)
> set_max_mapnr(max_pfn);
>
> So in the current implementation it checks against max_low_pfn while your
> patch checks against max_pfn
>
> max_low_pfn = max_pfn = memblock_end_of_DRAM() >> PAGE_SHIFT;
> #ifdef CONFIG_HIGHMEM
> max_low_pfn = lowmem_end_addr >> PAGE_SHIFT;
> #endif
Good point, I haven't considered CONFIG_HIGHMEM before.
As far as I understand it, in the non-CONFIG_HIGHMEM case:
- max_low_pfn is set to the same value as max_pfn, so the ioremap
check should detect the same PFNs as RAM.
and with CONFIG_HIGHMEM:
- max_low_pfn is set to lowmem_end_addr >> PAGE_SHIFT
- but max_pfn isn't
So, I think you're right.
While looking through arch/powerpc/mm, I noticed that there's a
page_is_ram function, which simply uses the memblocks directly, on
PPC32. It seems like a good candidate for the RAM check in
__ioremap_caller, except that there's this code, which apparently
trashes memblock 0 completely on non-CONFIG_NEED_MULTIPLE_NODES:
https://elixir.bootlin.com/linux/v4.16-rc2/source/arch/powerpc/mm/mem.c#L223
Thanks,
Jonathan Neuschäfer
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