On 04/22, Christian Borntraeger wrote: > > On 22/04/14 22:15, Christian Borntraeger wrote: > > On 21/04/14 15:25, Oleg Nesterov wrote: > >> async_pf_execute() has no reasons to adopt apf->mm, gup(current, mm) > >> should work just fine even if current has another or NULL ->mm. > >> > >> Recently kvm_async_page_present_sync() was added insedie the "use_mm" > >> section, but it seems that it doesn't need current->mm too. > >> > >> Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx> > > > > Indeed, use/unuse_mm should only be necessary for copy_to/from_user etc. > > This is fine for s390, but it seems that x86 kvm_arch_async_page_not_present > > might call apf_put_user which might call copy_to_user, so this is not ok, I guess. > > wanted to say kvm_arch_async_page_not_present, but I have to correct myself. > x86 does the "page is there" in the cpu loop, not in the worker. The cpu look > d oes have a valid mm. So this patch should be also ok. Thanks ;) Btw, I forgot to mention this in the changelog, but > >> @@ -80,12 +80,10 @@ static void async_pf_execute(struct work_struct *work) > >> > >> might_sleep(); > >> > >> - use_mm(mm); > >> down_read(&mm->mmap_sem); > >> get_user_pages(current, mm, addr, 1, 1, 0, NULL, NULL); > >> up_read(&mm->mmap_sem); > >> kvm_async_page_present_sync(vcpu, apf); > >> - unuse_mm(mm); it can actually do get_user_pages(NULL, mm, addr, 1, 1, 0, NULL, NULL); "task" is only used to increment task_struct->xxx_flt. I don't think async_pf_execute() actually needs this (current is PF_WQ_WORKER after all), but I didn't dare to do another change in the code I can hardly understand. Oleg. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
