Re: [PATCH v18] arm64: mm: Handle Granule Protection Faults (GPFs)

[Suzuki K Poulose]

On 22/09/2026 15:49, Catalin Marinas wrote:
> On Tue, Sep 22, 2026 at 02:21:13PM +0100, Suzuki K Poulose wrote:
> > I had another look and we could handle this via kvm_fault_is_gmem_abort()
> > see in arch/arm64/kvm/mmu.c:
> >
> >
> > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> > index 87e49251e0447..af5a4bf961aae 100644
> > --- a/arch/arm64/kvm/mmu.c
> > +++ b/arch/arm64/kvm/mmu.c
> > @@ -1731,6 +1731,9 @@ static int gmem_abort(const struct kvm_s2_fault_desc
> > *s2fd)
> >          gfn_t gfn;
> >          int ret;
> >
> > +       if (!kvm_slot_has_gmem(s2fd->memslot))
> > +               return -EINVAL;
>
> I wonder whether we should add a KVM_BUG_ON() here. With the rest of the
> changes, we should never get in this situation. Well, to be revisited
> for private devices.

Sure, I could add that

> Also maybe move it to the caller, kvm_vm_mem_abort(), and not change
> kvm_fault_is_gmem_abort(). Something like:
>
> 	if (private_ipa_fault(kvm, s2fd->fault_ipa) &&
> 	    KVM_BUG_ON(!kvm_slot_has_gmem(s2fd->memslot), kvm))
> 		return -EIO;
>
> To me it makes more sense for gmem_abort() to be called only *if* it's a
> gmem slot. So any inconsistency, avoiding user_mem_abort() for private
> memory, should be done in the caller. I assume the caller will also have
> to route the private device path as well rather than rely on
> gmem_abort().

Agree.

> > +
> >          if (!perm_fault) {
> >                  memcache = get_mmu_memcache(vcpu);
> >                  ret = topup_mmu_memcache(vcpu, memcache);
> > @@ -2277,10 +2280,12 @@ static bool private_ipa_fault(struct kvm *kvm,
> > phys_addr_t fault_ipa);
> >   static bool kvm_fault_is_gmem_abort(struct kvm *kvm,
> >                                      const struct kvm_s2_fault_desc *s2fd)
> >   {
> > -       if (!kvm_slot_has_gmem(s2fd->memslot))
> > -               return false;
> >          if (kvm_memslot_is_gmem_only(s2fd->memslot))
> >                  return true;
> > +       /*
> > +        * For Realms, all private faults must be backed by GMEM.
> > +        * TODO: Handle Trusted device private memory mappings.
> > +        */
> >          if (private_ipa_fault(kvm, s2fd->fault_ipa))
> >                  return true;
> >          return false;
> >
> >
> > Also, I have the following hunk for preventing memslot modifications.
> > I will add this to v20 integration branch, which is almost ready ;-)
> >
> > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> > index 582b48e34486b..87e49251e0447 100644
> > --- a/arch/arm64/kvm/mmu.c
> > +++ b/arch/arm64/kvm/mmu.c
> > @@ -2783,6 +2783,18 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
> >          }
> >   }
> >
> > +static bool kvm_prevents_memslot_change(struct kvm *kvm, enum kvm_mr_change change)
> > +{
> > +       /* Cannot modify memslots once a pVM has run or Realm created */
> > +       if (change != KVM_MR_DELETE && change != KVM_MR_MOVE)
> > +               return false;
> > +
> > +       if ((kvm_vm_is_protected_pkvm(kvm) && pkvm_hyp_vm_is_created(kvm)) ||
> > +            kvm_realm_is_created(kvm))
> > +               return true;
> > +       return false;
> > +}
> > +
> >   int kvm_arch_prepare_memory_region(struct kvm *kvm,
> >                                     const struct kvm_memory_slot *old,
> >                                     struct kvm_memory_slot *new,
> > @@ -2791,12 +2803,9 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
> >          hva_t hva, reg_end;
> >          int ret = 0;
> >
> > -       if (kvm_vm_is_protected_pkvm(kvm)) {
> > -               /* Cannot modify memslots once a pVM has run. */
> > -               if (pkvm_hyp_vm_is_created(kvm) &&
> > -                   (change == KVM_MR_DELETE || change == KVM_MR_MOVE)) {
> > +       if (kvm_vm_is_protected(kvm)) {
> > +               if (kvm_prevents_memslot_change(kvm, change))
> >                          return -EPERM;
> > -               }
> >
> >                  if (new &&
> >                      new->flags & (KVM_MEM_LOG_DIRTY_PAGES | KVM_MEM_READONLY)) {
>
> I think this should work.

Cheers
Suzuki

> Thanks.