On 01/25/2017 03:15 PM, Ahmed Samy wrote:
On Wed, Jan 25, 2017 at 02:27:27PM -0800, John Hubbard wrote:
Hi A. Samy,
I'm sorry this caught you by surprise, let's try get your use case covered.
My thinking on this was: the exported ioremap* family of functions was
clearly intended to provide just what the name says: mapping of IO (non-RAM)
memory. If normal RAM is to be re-mapped, then it should not be done
"casually" in a driver, as a (possibly unintended) side effect of a function
that implies otherwise. Either it should be done within the core mm code, or
perhaps a new, better-named wrapper could be provided, for cases such as
yours.
Hi John,
I agree. I assume whoever exported it was also doing it for the same
purpose as mine[?]
After a very quick peek at your github code, it seems that your mm_remap()
routine already has some code in common with __ioremap_caller(), so I'm
thinking that we could basically promote your mm_remap to the in-tree kernel
and EXPORT it, and maybe factor out the common parts (or not--it's small,
after all). Thoughts? If you like it, I'll put something together here.
That'd be a good solution, it's actually sometimes useful to remap physical
ram in general, specifically for memory imaging tools, etc.
How about also exporting walk_system_ram_range()? It seems to be defined
conditionally, so I am not sure if that would be a good idea.
That routine has an interesting history. At first glance, I think it used to be
exported. And now it is not. And it's ifdef'd out only for powerpc. I'll look into
the history and intentions of that some more...
[ See also mm_cache_ram_ranges() in mm.c in github – it's also a hacky
way to get RAM ranges. ]
Yes, I see.
How about something like:
/* vm_flags incase locking is required, in my case, I need it for VMX
* root where there is no interrupts. */
void *remap_ram_range(unsigned long phys, unsigned long size,
unsigned long vm_flags)
{
struct vm_struct *area;
unsigned long psize;
unsigned long vaddr;
psize = (size >> PAGE_SHIFT) + (size & (PAGE_SIZE - 1)) != 0;
area = get_vm_area_caller(size, VM_IOREMAP | vm_flags,
__builtin_return_address(0));
if (!area)
return NULL;
area->phys_addr = phys & ~(PAGE_SIZE - 1);
vaddr = (unsigned long)area->addr;
if (remap_page_range(vaddr, vaddr + size, phys, size))
That's ioremap_page_range, I assume (rather than remap_page_range)?
Overall, the remap_ram_range approach looks reasonable to me so far. I'll look into
the details tomorrow.
I'm sure that most people on this list already know this, but...could you say a few
more words about how remapping system ram is used, why it's a good thing and not a
bad thing? :)
thanks
john h
goto err_remap;
return (void *)vaddr + phys & (PAGE_SIZE - 1);
err_remap:
free_vm_area(area);
return NULL;
}
Of course you can add protection, etc.
thanks
john h
Thanks,
asamy
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