On Wed, 20 Dec 2017 14:17:24 +0100 Janosch Frank <frankja@xxxxxxxxxxxxxxxxxx> wrote: > On 20.12.2017 14:02, Cornelia Huck wrote: > > On Wed, 13 Dec 2017 13:53:32 +0100 > > Janosch Frank <frankja@xxxxxxxxxxxxxxxxxx> wrote: > > > >> KVM huge page backing support can not be easily tested under > >> s390. Currently testing is only possible after most of the guest has > >> already been set up. > >> > >> To indicate, that KVM has huge page backing support, we add the > >> KVM_CAP_S390_HPAGE capability. This does not mean, that transparent > >> huge pages are supported. > > > > Do you expect to use a different cap for non-1MB huge pages? If yes, > > this should probably be mentioned here. > > Yes probably KVM_CAP_S390_HPAGE2, but this will not come in the near future. > However this commit message lacks the information, that we only support > 1m pages, I'll add that. OK > > 1m guest backing pages ought to be enough for everybody (TM) :) > and the > pain to support 2g pages is expected to be a magnitude bigger than the > one for this patchset. This patchset already looks complicated enough to me... > > > > >> > >> Signed-off-by: Janosch Frank <frankja@xxxxxxxxxxxxxxxxxx> > >> --- > >> Documentation/virtual/kvm/api.txt | 10 ++++++++++ > >> arch/s390/kvm/kvm-s390.c | 1 + > >> include/uapi/linux/kvm.h | 1 + > >> 3 files changed, 12 insertions(+) > >> > >> diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt > >> index 57d3ee9..a56b0af 100644 > >> --- a/Documentation/virtual/kvm/api.txt > >> +++ b/Documentation/virtual/kvm/api.txt > >> @@ -4369,3 +4369,13 @@ Parameters: none > >> This capability indicates if the flic device will be able to get/set the > >> AIS states for migration via the KVM_DEV_FLIC_AISM_ALL attribute and allows > >> to discover this without having to create a flic device. > >> + > >> +8.14 KVM_CAP_S390_HPAGE > >> + > >> +Architectures: s390 > >> +This capability, if KVM_CHECK_EXTENSION indicates that it is > >> +available, means that KVM supports VMs that are memory backed through > >> +hugetlbfs with 1 megabyte pages. > >> + > >> +While it is generally possible to create and start a VM without this > >> +support, the VM will not be functional. > > > > This sentence applies only to the hugepage case, doesn't it? > > Yes, of course. > I'll do a: s/a/such a/ > > Expect a QEMU fencing patch next year. Sounds good!
