KVM: Let userspace disable per-VM mem attributes, enable per-gmem attributes

Allow the user to disable KVM_VM_MEMORY_ATTRIBUTES even when KVM supports
PRIVATE and SHARED attributes, and expose gmem_in_place_conversion as a
module parameter when per-VM attributes are supported.  I.e. let userspace
enable in-place PRIVATE<=>SHARED conversion of guest_memfd pages.

Provide both a Kconfig option and a (conditional) module param so that
deployments that use a custom kernel can fully disable per-VM tracking,
while not forcing distros to ship two separate kernels in order to provide
backwards compatibility for downstream users.

Don't allow running VMs with mixed tracking for a given instance of KVM,
i.e. disallow toggling the module param after KVM is loaded, as the extra
complexity needed to handle per-VM behavior far outweighs any potential
benefit.  E.g. neither TDX nor SNP supports live migration, so in effect
the requirement is that existing deployments that want to support both the
old and the new models would need to tell their VMM which flavor of
tracking to use.

[ Xiaoyao: Define module_param only if CONFIG_KVM_VM_MEMORY_ATTRIBUTES is enabled ]

Suggested-by: Xiaoyao Li <xiaoyao.li@intel.com>
Co-developed-by: Ackerley Tng <ackerleytng@google.com>
Signed-off-by: Ackerley Tng <ackerleytng@google.com>
Tested-by: Shivank Garg <shivankg@amd.com>
Reviewed-by: Fuad Tabba <tabba@google.com>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Tested-by: Yan Zhao <yan.y.zhao@intel.com>
Link: https://patch.msgid.link/20260910-gmem-inplace-conversion-v13-22-dd6fbf94f4e1@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

0 files changed, 0 insertions, 0 deletions