On Wed, 21 May 2025 at 11:26, David Hildenbrand <david@xxxxxxxxxx> wrote:
>
> On 21.05.25 12:12, Fuad Tabba wrote:
> > Hi David,
> >
> > On Wed, 21 May 2025 at 09:05, David Hildenbrand <david@xxxxxxxxxx> wrote:
> >>
> >> On 13.05.25 18:34, Fuad Tabba wrote:
> >>> Enable mapping guest_memfd in arm64. For now, it applies to all
> >>> VMs 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@xxxxxxxxxx>
> >>> ---
> >>> arch/arm64/include/asm/kvm_host.h | 10 ++++++++++
> >>> arch/arm64/kvm/Kconfig | 1 +
> >>> 2 files changed, 11 insertions(+)
> >>>
> >>> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> >>> index 08ba91e6fb03..2514779f5131 100644
> >>> --- a/arch/arm64/include/asm/kvm_host.h
> >>> +++ b/arch/arm64/include/asm/kvm_host.h
> >>> @@ -1593,4 +1593,14 @@ static inline bool kvm_arch_has_irq_bypass(void)
> >>> return true;
> >>> }
> >>>
> >>> +static inline bool kvm_arch_supports_gmem(struct kvm *kvm)
> >>> +{
> >>> + return IS_ENABLED(CONFIG_KVM_GMEM);
> >>> +}
> >>> +
> >>> +static inline bool kvm_arch_vm_supports_gmem_shared_mem(struct kvm *kvm)
> >>> +{
> >>> + return IS_ENABLED(CONFIG_KVM_GMEM_SHARED_MEM);
> >>> +}
> >>> +
> >>> #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.
> >>>
> >>
> >> Do we have to reject somewhere if we are given a guest_memfd that was
> >> *not* created using the SHARED flag? Or will existing checks already
> >> reject that?
> >
> > We don't reject, but I don't think we need to. A user can create a
> > guest_memfd that's private in arm64, it would just be useless.
>
> But the arm64 fault routine would not be able to handle that properly, no?
Actually it would. The function user_mem_abort() doesn't care whether
it's private or shared. It would fault it into the guest correctly
regardless.
Thanks,
/fuad
> --
> Cheers,
>
> David / dhildenb
>
