Re: [PATCH v12 09/45] KVM: guest_memfd: Stub in ability to enable in-place shared<=>private conversion

[Binbin Wu]

On 8/31/2026 8:25 AM, Ackerley Tng via B4 Relay wrote:
> From: Sean Christopherson <seanjc@xxxxxxxxxx>
> 
> Stub in global variable to enable in-place guest_memfd private<=>shared
> memory conversion, which will eventually be exposed to userspace via a
> module param, and wire up the __kvm_is_private_gfn() static call to the
> guest_memfd version when in-place conversion is enabled, i.e. when gmem is
> the sole authority on private vs. shared memory.
> 
> Cc: Fuad Tabba <tabba@xxxxxxxxxx>
> Cc: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> Co-developed-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>
> Signed-off-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>

Reviewed-by: Binbin Wu <binbin.wu@xxxxxxxxxxxxxxx>

One nit below.

> ---
>  Documentation/virt/kvm/api.rst |  7 +++++++
>  include/linux/kvm_host.h       |  6 ++++++
>  virt/kvm/guest_memfd.c         | 26 ++++++++++++++++++++++++++
>  virt/kvm/kvm_main.c            | 12 +++++++++++-
>  4 files changed, 50 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> index e0430cc750c9e..90a29424c54c8 100644
> --- a/Documentation/virt/kvm/api.rst
> +++ b/Documentation/virt/kvm/api.rst
> @@ -6382,6 +6382,11 @@ KVM_SET_USER_MEMORY_REGION2, e.g. shared memory can be lazily mapped/allocated
>  on-demand.
>  
>  When mapping a gfn into the guest, KVM selects shared vs. private, i.e consumes
> +userspace_addr vs. guest_memfd, based on the state in guest_memfd, which is the
> +sole authority on private vs. shared memory.  See :ref:`KVM_CREATE_GUEST_MEMFD`
> +to find out more about the creation-time shared/private status.
> +
> +If in-place conversion is disabled, KVM selects shared vs. private, i.e consumes

Nit: i.e -> i.e.
>  userspace_addr vs. guest_memfd, based on the gfn's KVM_MEMORY_ATTRIBUTE_PRIVATE
>  state.  At VM creation time, all memory is shared, i.e. the PRIVATE attribute
>  is '0' for all gfns.  Userspace can control whether memory is shared/private by
> @@ -6429,6 +6434,8 @@ the state of a gfn/page as needed.
>