Hi Suzuki,
On Tue, 15 Oct 2024 at 11:30, Suzuki K Poulose <suzuki.poulose@xxxxxxx> wrote:
>
> Hi Fuad
>
> On 10/10/2024 09:59, Fuad Tabba wrote:
> > Add the KVM capability KVM_CAP_GUEST_MEMFD_MAPPABLE, which is
> > true if mapping guest memory is supported by the host.
> >
> > Signed-off-by: Fuad Tabba <tabba@xxxxxxxxxx>
> > ---
> > include/uapi/linux/kvm.h | 1 +
> > virt/kvm/kvm_main.c | 4 ++++
> > 2 files changed, 5 insertions(+)
> >
> > diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> > index 637efc055145..2c6057bab71c 100644
> > --- a/include/uapi/linux/kvm.h
> > +++ b/include/uapi/linux/kvm.h
> > @@ -933,6 +933,7 @@ struct kvm_enable_cap {
> > #define KVM_CAP_PRE_FAULT_MEMORY 236
> > #define KVM_CAP_X86_APIC_BUS_CYCLES_NS 237
> > #define KVM_CAP_X86_GUEST_MODE 238
> > +#define KVM_CAP_GUEST_MEMFD_MAPPABLE 239
> >
> > struct kvm_irq_routing_irqchip {
> > __u32 irqchip;
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index 77e6412034b9..c2ff09197795 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -5176,6 +5176,10 @@ static int kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg)
> > #ifdef CONFIG_KVM_PRIVATE_MEM
> > case KVM_CAP_GUEST_MEMFD:
> > return !kvm || kvm_arch_has_private_mem(kvm);
> > +#endif
> > +#ifdef CONFIG_KVM_GMEM_MAPPABLE
> > + case KVM_CAP_GUEST_MEMFD_MAPPABLE:
> > + return !kvm || kvm_arch_has_private_mem(kvm);
>
> minor nit: Keying this on whether the "kvm" instance has private mem
> may not be flexible enough to support other types of CC guest that
> may use guestmem, but not "mappable" memory. e.g. CCA may not
> support "mappable", unless we have a way to explicitly pass down
> "you can map a shared page from the guest_memfd, but it is not
> sharable in place".
>
> We could solve it when we get there, but it might be worth
> considering.
I did consider that, but I assumed that the configuration option would
be sufficient. Otherwise, we could make it dependent on the VM type.
Cheers,
/fuad
> Suzuki
>
>
>
>
> > #endif
> > default:
> > break;
>
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