On Thu, 29 Jul 2021 12:49:03 +0200 Cornelia Huck <cohuck@xxxxxxxxxx> wrote: > On Wed, Jul 28 2021, Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx> wrote: > > > Improve make_secure_pte to avoid stalls when the system is heavily > > overcommitted. This was especially problematic in > > kvm_s390_pv_unpack, because of the loop over all pages that needed > > unpacking. > > > > Also fix kvm_s390_pv_init_vm to avoid stalls when the system is > > heavily overcommitted. > > > > Signed-off-by: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx> > > --- > > arch/s390/kernel/uv.c | 11 ++++++++--- > > arch/s390/kvm/pv.c | 2 +- > > 2 files changed, 9 insertions(+), 4 deletions(-) > > > > diff --git a/arch/s390/kernel/uv.c b/arch/s390/kernel/uv.c > > index aeb0a15bcbb7..fd0faa51c1bb 100644 > > --- a/arch/s390/kernel/uv.c > > +++ b/arch/s390/kernel/uv.c > > @@ -196,11 +196,16 @@ static int make_secure_pte(pte_t *ptep, > > unsigned long addr, if (!page_ref_freeze(page, expected)) > > return -EBUSY; > > set_bit(PG_arch_1, &page->flags); > > - rc = uv_call(0, (u64)uvcb); > > + rc = __uv_call(0, (u64)uvcb); > > page_ref_unfreeze(page, expected); > > - /* Return -ENXIO if the page was not mapped, -EINVAL > > otherwise */ > > - if (rc) > > + /* > > + * Return -ENXIO if the page was not mapped, -EINVAL for > > other errors. > > + * If busy or partially completed, return -EAGAIN. > > + */ > > + if (rc == 1) > > rc = uvcb->rc == 0x10a ? -ENXIO : -EINVAL; > > + else if (rc > 1) > > + rc = -EAGAIN; > > return rc; > > } > > Possibly dumb question: when does the call return > 1? this is exactly what Janosch meant :) the next version will have #defines for the 4 possible CC values. in short: 0 OK 1 error 2 busy (nothing done, try again) 3 partial (something done but not all, try again) > gmap_make_secure() will do a wait_on_page_writeback() for -EAGAIN, is > that always the right thing to do? it's the easiest way to get to a place where we will be able to reschedule if needed. wait_on_page_writeback will probably do nothing in that case because the page is not in writeback. (a few minutes later) actually I have checked, it seems that the -EAGAIN gets eventually propagated to places where it's not checked properly! this will need some more fixing
