Re: [RFC PATCH v2 04/10] KVM: Add KVM capability to check if guest_memfd can be mapped by the host

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Hi Ackerley,

On Mon, 5 Aug 2024 at 18:19, Ackerley Tng <ackerleytng@xxxxxxxxxx> wrote:
>
> Fuad Tabba <tabba@xxxxxxxxxx> writes:
>
> > 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 | 3 ++-
> >  virt/kvm/kvm_main.c      | 4 ++++
> >  2 files changed, 6 insertions(+), 1 deletion(-)
> >
> > <snip>
>
> Why do we need a cap for `KVM_CAP_GUEST_MEMFD_MAPPABLE` instead of just
> making guest_memfd mmap-able?
>
> Is this to prevent breaking userspace, because a user might be relying
> on guest_memfd being not mmap-able?

To be able to check that the ability is there, since it is a new
capability not available in Linux 6.9 not 6.10 (i.e., after
guest_memfd()) was introduced.

Cheers,
/fuad




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