[PATCH RFC v5 25/53] KVM: TDX: Make source page optional for KVM_TDX_INIT_MEM_REGION

Ackerley Tng via B4 Relay
2026-04-28T23:25:19Z

Update tdx_gmem_post_populate() to handle cases where a source page is
not explicitly provided. Instead of returning -EOPNOTSUPP when src_page
is NULL, default to using the page associated with the destination PFN.

This change allows for in-place memory conversion where the data is
already present in the target PFN, ensuring the TDX module has a valid
source page reference for the TDH.MEM.PAGE.ADD operation.

Signed-off-by: Ackerley Tng <ackerleytng@google.com>
---
Documentation/virt/kvm/x86/intel-tdx.rst | 4 ++++
arch/x86/kvm/vmx/tdx.c | 8 ++++++--
2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/Documentation/virt/kvm/x86/intel-tdx.rst b/Documentation/virt/kvm/x86/intel-tdx.rst
index 6a222e9d09541..fbc0f179dc750 100644
--- a/Documentation/virt/kvm/x86/intel-tdx.rst
+++ b/Documentation/virt/kvm/x86/intel-tdx.rst
@@ -158,6 +158,10 @@ KVM_TDX_INIT_MEM_REGION
Initialize @nr_pages TDX guest private memory starting from @gpa with userspace
provided data from @source_addr. @source_addr must be PAGE_SIZE-aligned.

+If memory attributes are tracked in guest_memfd, pass NULL for
+@source_addr to initialize the memory region using memory contents
+already populated in guest_memfd memory.
+
Note, before calling this sub command, memory attribute of the range
[gpa, gpa + nr_pages] needs to be private. Userspace can use
KVM_SET_MEMORY_ATTRIBUTES to set the attribute.
diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index 04ce321ebdf39..10373e606242a 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -3116,8 +3116,12 @@ static int tdx_gmem_post_populate(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn,
if (KVM_BUG_ON(kvm_tdx->page_add_src, kvm))
return -EIO;

- if (!src_page)
- return -EOPNOTSUPP;
+ if (!src_page) {
+ if (vm_memory_attributes)
+ return -EOPNOTSUPP;
+
+ src_page = pfn_to_page(pfn);
+ }

kvm_tdx->page_add_src = src_page;
ret = kvm_tdp_mmu_map_private_pfn(arg->vcpu, gfn, pfn);

--
2.54.0.545.g6539524ca2-goog