From: Mikael Pettersson <mikpe@xxxxxxxx> Date: Thu, 6 Jul 2006 11:37:35 +0200 (MEST) > On Wed, 05 Jul 2006 20:40:36 -0700 (PDT), David Miller wrote: > >> I.e., X did a simple PROT_READ|PROT_WRITE MAP_SHARED mmap() of > >> something PCI-related, presumably the ATI card. The protection > >> bits passed into io_remap_pfn_range() are 0x80...0788, while > >> pg_iobits are 0x80...0f8a. Current kernels obey the prot bits, > >> which, if I read things correctly, means that _PAGE_W_4U and > >> _PAGE_MODIFIED_4U don't get set any more. > >> > >> I guess something else in the kernel should have set those > >> bits before they got to io_remap_pfn_range()? > > > >The problem is with X, it should not be doing a MAP_SHARED > >mmap() of the framebuffer device. It should be using > >MAP_PRIVATE instead. > > > >The kernel is trying to provide copy-on-write semantics for > >the mapping, which doesn't make any sense for device registers. > >That's why the kernel isn't setting the writable or modified > >bits in the protection bitmask. > > Now I'm confused. That COW behaviour would be consistent with > MAP_PRIVATE, not MAP_SHARED which is what X did use. Yes, I'm totally wrong here, MAP_SHARED is correct. I'll have to figure out how the writeable bits get lost in the call chain. Thanks. - To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
