On Wed, 9 Mar 2016, Ingo Molnar wrote: > > > So to go back to the original suggestion from Luis, I've quoted it, but > > > with a s/overlapping/aliased substitution: > > > > > > > I had suggested long ago then that one possible resolution was for us > > > > to add an API that *enables* aliased ioremap() calls, and only use it > > > > on select locations in the kernel. This means we only have to convert a > > > > few users to that call to white list such semantics, and by default > > > > we'd disable aliased calls. To kick things off -- is this strategy > > > > agreeable for all other architectures? > > > > > > I'd say that since the overwhelming majority of ioremap() calls are not > > > aliased, ever, thus making it 'harder' to accidentally alias is probably > > > a good idea. > > > > Did you mean 'aliased' or 'aliased with different cache attribute'? The > > former > > check might be too strict. > > I'd say even 'same attribute' aliasing is probably relatively rare.
Please note that aliased cached mappings (any kinds of, not necessarily from `ioremap') cause a lot of headache (read: handling trouble) with architectures such as MIPS which support virtually indexed caches which suffer from cache aliasing. There is a risk of data corruption if the same physical memory address space location is accessed through different virtual mappings as not all hardware catches duplicate cache entries created in such a case. We handle it in software for user mappings (although I keep having a feeling something always keeps escaping, due to the vast diversity of cache configurations possible), however I don't think we do for `ioremap', so disallowing aliased `ioremap' mappings by default sounds like a good idea to me. FWIW, Maciej
