Re: Access to non-RAM pages

From: Jiri Kosina
Date: Fri Aug 31 2018 - 18:02:51 EST

On Wed, 29 Aug 2018, Juergen Gross wrote:

> While being very unlikely I still believe this is possible. Any
> thoughts?

So in theory we should somehow test whether the next page is some form of
mmio/gart/... mapping, but I guess that by itself would kill the
performance advantage of the whole load_unaligned_zeropad() trick.

And yes, the sideffects of reading from mmio mapping is a real thing --
see for example the issue fixed by 2a3e83c6f9.

If noone has any clever idea how to work this around (I don't), I am
afraid we'd have to ditch the whole DCACHE_WORD_ACCESS optimization, as
it's silently dangerous.


Jiri Kosina