Re: [PATCH v9 14/17] KVM: arm64: Enable mapping guest_memfd in arm64

[Fuad Tabba <tabba@google.com>]

Hi James,

On Fri, 16 May 2025 at 01:51, James Houghton <jthoughton@google.com> wrote:
>
> On Tue, May 13, 2025 at 9:35 AM Fuad Tabba <tabba@google.com> 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@google.com>
> > ---
> >  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);
> > +}
>
> This is written as if it is okay for CONFIG_KVM_GMEM not to be
> enabled, but when disabling CONFIG_KVM_GMEM you will get an error for
> redefining kvm_arch_supports_gmem().
>
> I think you either want to include:
>
> #define kvm_arch_supports_gmem kvm_arch_supports_gmem
>
> or just do something closer to what x86 does:
>
> #ifdef CONFIG_KVM_GMEM
> #define kvm_arch_supports_gmem(kvm) true
> #endif
> > +
> > +static inline bool kvm_arch_vm_supports_gmem_shared_mem(struct kvm *kvm)
> > +{
> > +       return IS_ENABLED(CONFIG_KVM_GMEM_SHARED_MEM);
> > +}
>
> And this applies here as well.
>
> #define kvm_arch_vm_supports_gmem_shared_mem
> kvm_arch_vm_supports_gmem_shared_mem
>
> or
>
> #ifdef CONFIG_KVM_GMEM
> #define kvm_arch_vm_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
>
> This makes it impossible to see the error, but I think we should fix
> it anyway. :)

Ack.

Thank you!
/fuad

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> >
> > --
> > 2.49.0.1045.g170613ef41-goog
> >