On Wed, 22 Oct 2014 12:09:31 +0200 Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote: > On 10/22/2014 10:30 AM, Dominik Dingel wrote: > > As use_skey is already the condition on which we call s390_enable_skey > > we need to introduce a new flag for the mm->context on which we decide > > if zero page mapping is allowed. > > Can you explain better why "mm->context.use_skey = 1" cannot be done > before the walk_page_range? Where does the walk or __s390_enable_skey > or (after the next patch) ksm_madvise rely on > "mm->context.forbids_zeropage && !mm->context.use_skey"? I can't, my reasoning there is wrong. I remembered incorrectly that we use mm_use_skey in arch/s390/kvm/priv.c to check if we need to call s390_enable_skey, but that does happen with the interception bits. So every vCPU which get the a interception for a storage key instruction will call s390_enable_skey and wait there for the mmap_sem. > The only reason I can think of, is that the next patch does not reset > "mm->context.forbids_zeropage" to 0 if the ksm_madvise fails. Why > doesn't it do that---or is it a bug? You are right, this is a bug, where we will drop to userspace with -ENOMEM. I will fix this as well. > Thanks, and sorry for the flurry of questions! :) I really appreciate your questions and remarks. Thank you! > Paolo > -- 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>