KVM: TDX: Make source page optional for KVM_TDX_INIT_MEM_REGION

Update tdx_gmem_post_populate() to handle cases where userspace requests
"no source page". To handle "no source page", populate (perform
TDH.MEM.PAGE.ADD) using memory in-place at the target PFN.

Allow "no source page" only when gmem_in_place_conversion is enabled,
because retroactively adding support for out-of-place conversion would mean
requiring a userspace update for a feature that's being deprecated.

Also, KVM supporting "no source page" without in-place conversion would
effectively be an obscure zero-page optimization that relies on the page
being zeroed when it is allocated by guest_memfd.

Rejecting "no source page" without in-place conversion scenario is valuable
for KVM developers since it helps newcomers understand what exactly is and
isn't possible.

Co-developed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Ackerley Tng <ackerleytng@google.com>
Tested-by: Shivank Garg <shivankg@amd.com>
Tested-by: Yan Zhao <yan.y.zhao@intel.com>
Reviewed-by: Binbin Wu <binbin.wu@linux.intel.com>
Reviewed-by: Yan Zhao <yan.y.zhao@intel.com>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Link: https://patch.msgid.link/20260910-gmem-inplace-conversion-v13-20-dd6fbf94f4e1@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

0 files changed, 0 insertions, 0 deletions