On Wed, 2014-09-10 at 15:34 -0600, Toshi Kani wrote: > On Wed, 2014-09-10 at 13:29 -0700, Andy Lutomirski wrote: > > On Wed, Sep 10, 2014 at 1:12 PM, Toshi Kani <toshi.k...@hp.com> wrote: > > > On Wed, 2014-09-10 at 11:30 -0700, Andy Lutomirski wrote: > > >> On Wed, Sep 10, 2014 at 9:51 AM, Toshi Kani <toshi.k...@hp.com> wrote: > > >> > +Drivers may map the entire NV-DIMM range with ioremap_cache and then > > >> > change > > >> > +a specific range to wt with set_memory_wt. > > >> > > >> That's mighty specific :) > > > > > > How about below? > > > > > > Drivers may use set_memory_wt to set WT type for cached reserve ranges. > > > > Do they have to be cached? > > Yes, set_memory_xyz only supports WB->type->WB transition. > > > How about: > > > > Drivers may call set_memory_wt on ioremapped ranges. In this case, > > there is no need to change the memory type back before calling > > iounmap. > > > > (Or only on cached ioremapped ranges if that is, in fact, the case.) > > Sounds good. Yes, I will use cashed ioremapped ranges.
Well, testing "no need to change the memory type back before calling iounmap" turns out to be a good test case. I realized that set_memory_xyz only works properly for RAM. There are two problems for using this interface for ioremapped ranges. 1) set_memory_xyz calls reserve_memtype() with __pa(addr). However, __pa() translates the addr into a fake physical address when it is an ioremapped address. 2) reserve_memtype() does not work for set_memory_xyz. For RAM, the WB state is managed untracked. Hence, WB->new->WB is not considered as a conflict. For ioremapped ranges, WB is tracked in the same way as other cache types. Hence, WB->new is considered as a conflict. In my previous testing, 2) was undetected since 1) led using a fake physical address which was not tracked for WB. This made ioremapped ranges worked just like RAM. :-( Anyway, 1) can be fixed by using slow_virt_to_phys() instead of __pa(). set_memory_xyz is already slow, but this makes it even slower, though. For 2), WB has to be continuously tracked in order to detect aliasing, ex. ioremap_cache and ioremap to a same address. So, I think reserve_memtype() needs the following changes: - Add a new arg to see if an operation is to create a new mapping or to change cache attribute. - Track overlapping maps so that cache type change to an overlapping range can be detected and failed. This level of changes requires a separate set of patches if we pursue to support ioremapped ranges. So, I am considering to take one of the two options below. A) Drop the patch for set_memory_wt. B) Keep the patch for set_memory_wt, but document that it fails with -EINVAL and its use is for RAM only. Any suggestion? Thanks, -Toshi -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
