linux-kernel - [PATCH 2/3] KVM: TDX: Document alignment requirements for KVM_TDX_INIT_MEM

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Message-ID: <20251113230759.1562024-3-michael.roth@amd.com>
Date: Thu, 13 Nov 2025 17:07:58 -0600
From: Michael Roth <michael.roth@....com>
To: <kvm@...r.kernel.org>
CC: <linux-coco@...ts.linux.dev>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>, <thomas.lendacky@....com>,
	<pbonzini@...hat.com>, <seanjc@...gle.com>, <vbabka@...e.cz>,
	<ashish.kalra@....com>, <liam.merwick@...cle.com>, <david@...hat.com>,
	<vannapurve@...gle.com>, <ackerleytng@...gle.com>, <aik@....com>,
	<ira.weiny@...el.com>, <yan.y.zhao@...el.com>
Subject: [PATCH 2/3] KVM: TDX: Document alignment requirements for KVM_TDX_INIT_MEM_REGION

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@....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