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SubjectRe: can device drivers return non-ram via vm_ops->nopage?


On Sat, 20 Mar 2004, Andrea Arcangeli wrote:
>
> The only bugreport I've got so far for the latest anon_vma code is from
> Jens, and it's a device driver bug in my opinion, but I'd like to have a
> definitive confirmation from you about the ->nopage API.

I'd say that this is definitely a driver bug.

If a driver wants to map non-RAM pages, that's perfectly ok, but it MUST
NOT happen through "nopage()". The driver should map them with
"remap_page_range()", and thus never take a page fault for such pages at
all.

There is no reason to ever lazily map non-RAM pages - clearly they aren't
using any "real memory", so there is no reason to not fill the page tables
at mmap() time.

In other words, the driver is horribly broken.

Linus
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