On Tue, 2015-07-07 at 18:07 +0200, Luis R. Rodriguez wrote: > On Tue, Jul 07, 2015 at 11:13:30AM +0100, Russell King - ARM Linux > wrote: : > > On ARM, we (probably) have a lot of cases where ioremap() is used > > multiple > > times for the same physical address space, so we shouldn't rule out > > having > > multiple mappings of the same type. > > Why is that done? Don't worry if you are not sure why but only > speculate of the > practice's existence (sloppy drivers or lazy driver developers). FWIW > for x86 > IIRC I ended up concluding that overlapping ioremap() calls with the > same type > would work but not if they differ in type. Although I haven't > written a > grammer rule to hunt down overlapping ioremap() I suspected its use > was likely > odd and likely should be reconsidered. Would this be true for ARM too > ? Or are > you saying this should be a feature ? I don't expect an answer now > but I'm > saying we *should* all together decide on this, and if you're > inclined to > believe that this should ideally be avoided I'd like to hear that. If > you feel > strongly though this should be a feature I would like to know why. There are multiple mapping interfaces, and overlapping can happen among them as well. For instance, remap_pfn_range() (and io_remap_pfn_range(), which is the same as remap_pfn_range() on x86) creates a mapping to user space. The same physical ranges may be mapped to kernel and user spaces. /dev/mem is one example that may create a user space mapping to a physical address that is already mapped with ioremap() by other module. pmem and DAX also create mappings to the same NVDIMM ranges. DAX calls vm_insert_mixed(), which is particularly a problematic since vm_insert_mixed() does not verify aliasing. ioremap() and remap_pfn_range() call reserve_memtype() to verify aliasing on x86. reserve_memtype() is x86-specific and there is no arch-generic wrapper for such check. I think DAX could get a cache type from pmem to keep them in sync, though. Thanks, -Toshi -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>