On Sat, 2010-03-06 at 19:36 +0000, Russell King - ARM Linux wrote: > On Sat, Mar 06, 2010 at 04:17:23PM +0530, James Bottomley wrote: > > On a fault in of exec data, we first try to get the page out of the page > > cache. If it's not present, we put the faulting process to sleep and > > fetch it in from storage. When we do the read, on the PIO path, the > > kernel alias for the page becomes dirty. Some time later, we place the > > page into the user space (updating the pte entry that caused a fault). > > At this point, we'll call both flush_icache_page() and > > update_mmu_cache() ... this is where the I/D resolution should be done. > > No - this is where things get extremely icky. > > The problem at this point occurs on SMP architectures. As soon as you > update the PTE entry, it is visible to other threads of the application. > If you do I-cache handling after updating the PTE, then there is a window > where another CPU can execute the page: Right, we actually hit that bug on powerpc, however, James explanation is misleading, ie, I think the -code- actually is right and flush_icache_page() is called before set_pte_at(). However, see my other email, I have other issues with it as it is, but nothing unfixable. So for now, I keep my flush in set_pte_at() and ptep_set_access_flags(), we'll see if I can move that to an improved flush_icache_page(). In fact, even set_pte_at() isn't a panacea for me, as I want the fault type as well. Cheers, Ben. > CPU0 CPU1 > speculatively prefetches from page N via kernel > mapping, loads garbage into I-cache > attempts to execute P > page fault > page N allocated > set_pte_at > executes P > *splat* > flush I-cache -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
