Re: [PATCH v3 15/23] KVM: s390: Add helper functions for fault handling

Claudio Imbrenda
2025-11-19T11:06:22Z

On Tue, 18 Nov 2025 16:10:05 +0100
Heiko Carstens <hca@linux.ibm.com> wrote:

> On Thu, Nov 06, 2025 at 05:11:09PM +0100, Claudio Imbrenda wrote:
> > Add some helper functions for handling multiple guest faults at the
> > same time.
> >
> > This will be needed for VSIE, where a nested guest access also needs to
> > access all the page tables that map it.
> >
> > Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
> > ---
> > arch/s390/include/asm/kvm_host.h | 1 +
> > arch/s390/kvm/Makefile | 2 +-
> > arch/s390/kvm/faultin.c | 148 +++++++++++++++++++++++++++++++
> > arch/s390/kvm/faultin.h | 92 +++++++++++++++++++
> > arch/s390/kvm/kvm-s390.c | 2 +-
> > arch/s390/kvm/kvm-s390.h | 2 +
> > 6 files changed, 245 insertions(+), 2 deletions(-)
> > create mode 100644 arch/s390/kvm/faultin.c
> > create mode 100644 arch/s390/kvm/faultin.h
>
> ...
>
> > +int kvm_s390_faultin_gfn(struct kvm_vcpu *vcpu, struct kvm *kvm, struct guest_fault *f)
> > +{
>
> ...
>
> > + scoped_guard(read_lock, &kvm->mmu_lock) {
> > + if (!mmu_invalidate_retry_gfn(kvm, inv_seq, f->gfn)) {
> > + f->valid = true;
> > + rc = gmap_link(mc, kvm->arch.gmap, f);
> > + kvm_release_faultin_page(kvm, f->page, !!rc, f->write_attempt);
> > + f->page = NULL;
> > + }
> > + }
> > + kvm_release_faultin_page(kvm, f->page, true, false);
> > +
> > + if (rc == -ENOMEM) {
> > + rc = kvm_s390_mmu_cache_topup(mc);
>
> If I'm not mistaken then gmap_link() -> dat_link() maps the possible -ENOMEM
> return value of dat_entry() to -EAGAIN. So the case where -ENOMEM leads to a
> kvm_s390_mmu_cache_topup() call will never happen.

oops, you're right

I'll fix dat_link() accordingly