Re: [PATCH v10 14/16] KVM: arm64: Enable mapping guest_memfd in arm64

[Fuad Tabba <tabba@google.com>]

On Wed, 4 Jun 2025 at 14:17, David Hildenbrand <david@redhat.com> wrote:
>
> On 27.05.25 20:02, Fuad Tabba wrote:
> > Enable mapping guest_memfd backed memory at the host in arm64. For now,
> > it applies to all arm64 VM types in arm64 that use guest_memfd. In the
> > future, new VM types can restrict this via
> > kvm_arch_gmem_supports_shared_mem().
> >
> > Signed-off-by: Fuad Tabba <tabba@google.com>
> > ---
> >   arch/arm64/include/asm/kvm_host.h | 5 +++++
> >   arch/arm64/kvm/Kconfig            | 1 +
> >   arch/arm64/kvm/mmu.c              | 7 +++++++
> >   3 files changed, 13 insertions(+)
> >
> > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> > index 08ba91e6fb03..8add94929711 100644
> > --- a/arch/arm64/include/asm/kvm_host.h
> > +++ b/arch/arm64/include/asm/kvm_host.h
> > @@ -1593,4 +1593,9 @@ static inline bool kvm_arch_has_irq_bypass(void)
> >       return true;
> >   }
> >
> > +#ifdef CONFIG_KVM_GMEM
> > +#define kvm_arch_supports_gmem(kvm) true
> > +#define kvm_arch_supports_gmem_shared_mem(kvm) IS_ENABLED(CONFIG_KVM_GMEM_SHARED_MEM)
> > +#endif
> > +
> >   #endif /* __ARM64_KVM_HOST_H__ */
> > diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
> > index 096e45acadb2..8c1e1964b46a 100644
> > --- a/arch/arm64/kvm/Kconfig
> > +++ b/arch/arm64/kvm/Kconfig
> > @@ -38,6 +38,7 @@ menuconfig KVM
> >       select HAVE_KVM_VCPU_RUN_PID_CHANGE
> >       select SCHED_INFO
> >       select GUEST_PERF_EVENTS if PERF_EVENTS
> > +     select KVM_GMEM_SHARED_MEM
> >       help
> >         Support hosting virtualized guest machines.
> >
> > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> > index 896c56683d88..03da08390bf0 100644
> > --- a/arch/arm64/kvm/mmu.c
> > +++ b/arch/arm64/kvm/mmu.c
> > @@ -2264,6 +2264,13 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
> >       if ((new->base_gfn + new->npages) > (kvm_phys_size(&kvm->arch.mmu) >> PAGE_SHIFT))
> >               return -EFAULT;
> >
> > +     /*
> > +      * Only support guest_memfd backed memslots with shared memory, since
> > +      * there aren't any CoCo VMs that support only private memory on arm64.
> > +      */
> > +     if (kvm_slot_has_gmem(new) && !kvm_gmem_memslot_supports_shared(new))
> > +             return -EINVAL;
> > +
>
> Right, that can get lifted once we have such VMs.
>
> Acked-by: David Hildenbrand <david@redhat.com>

Thanks!
/fuad

> --
> Cheers,
>
> David / dhildenb
>