On Sat, 2013-11-16 at 21:07 +0100, Simon Baatz wrote: > On Fri, Nov 15, 2013 at 02:42:05PM -0800, James Bottomley wrote: > > On Fri, 2013-11-15 at 23:05 +0100, Helge Deller wrote: > > > When a user page mapping is released via kunmap*() functions, the D-cache needs > > > to be flushed via flush_dcache_page() to avoid D-cache aliasing issues. > > > > > > This patch fixes aio on the parisc platform (and probably others). > > > > This should be flush_kernel_dcache_page(). flush_dcache_page() is for > > full coherency but for unmap, we know the page was coherent going in and > > may have been modified by the kernel, so only the kernel view needs to > > be sync'd. Technically, by the kernel API, the flush should be done > > *before* unmapping. This would have mattered on parisc until we did > > flush via tmpalias which means we no-longer care if the mapping for the > > flush exists or not because we always recreate it via the tmpalias > > pages. > > On ARM, flush_kernel_dcache_page() actually assumes that the page is > mapped. It avoids double flushing of highmem pages by not flushing > in those cases where kunmap_atomic() already takes care of flushing. On Parisc, kmap/kunmap is currently a nop. However, if we ever implemented highmem, we would also need to flush before we unmap, which is why the flush needs to go before the kunmap. I've got to say on all of this, we've implemented the most inane set of primitives. It would be much easier if kmap/kunmap just took care of all of this. kmap should bring userspace into coherence (because why else would we be kmapping) and kunmap should force coherence on the kernel address ... and then no-one would need to worry when to and when not to flush. James -- To unsubscribe from this list: send the line "unsubscribe linux-parisc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
