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

[Ackerley Tng via B4 Relay <devnull+ackerleytng.google.com@kernel.org>]

From: Ackerley Tng <ackerleytng@google.com>

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