[PATCH 2/3] KVM: TDX: Document alignment requirements for KVM_TDX_INIT_MEM_REGION

Michael Roth
2025-11-13T23:09:03Z

Since it was never possible to use a non-PAGE_SIZE-aligned @source_addr,
go ahead and document this as a requirement, and add a KVM_BUG_ON() in
the post-populate callback handler to ensure future reworks to
guest_memfd do not violate this constraint.

Signed-off-by: Michael Roth <michael.roth@amd.com>
---
Documentation/virt/kvm/x86/intel-tdx.rst | 2 +-
arch/x86/kvm/vmx/tdx.c | 3 +++
2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/Documentation/virt/kvm/x86/intel-tdx.rst b/Documentation/virt/kvm/x86/intel-tdx.rst
index 5efac62c92c7..6a222e9d0954 100644
--- a/Documentation/virt/kvm/x86/intel-tdx.rst
+++ b/Documentation/virt/kvm/x86/intel-tdx.rst
@@ -156,7 +156,7 @@ KVM_TDX_INIT_MEM_REGION
:Returns: 0 on success, <0 on error

Initialize @nr_pages TDX guest private memory starting from @gpa with userspace
-provided data from @source_addr.
+provided data from @source_addr. @source_addr must be PAGE_SIZE-aligned.

Note, before calling this sub command, memory attribute of the range
[gpa, gpa + nr_pages] needs to be private. Userspace can use
diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index 3cf80babc3c1..57ed101a1181 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -3127,6 +3127,9 @@ 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 (KVM_BUG_ON(!PAGE_ALIGNED(src), kvm))
+ return -EINVAL;
+
/*
* Get the source page if it has been faulted in. Return failure if the
* source page has been swapped out or unmapped in primary memory.
--
2.25.1