On Thu, Jun 18, 2026 at 05:32:00PM -0700, Ackerley Tng via B4 Relay wrote:
> From: Ackerley Tng <[email protected]>
>
> 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 <[email protected]>
> Signed-off-by: Sean Christopherson <[email protected]>
> ---
> Documentation/virt/kvm/x86/intel-tdx.rst | 4 ++++
> arch/x86/kvm/vmx/tdx.c | 11 ++++++++---
> 2 files changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/virt/kvm/x86/intel-tdx.rst
> b/Documentation/virt/kvm/x86/intel-tdx.rst
> index 6a222e9d09541..74357fe87f9ec 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 guest_memfd in-place conversion is enabled, 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 ffe9d0db58c59..56d10333c61a7 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -3198,8 +3198,12 @@ 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 (!gmem_in_place_conversion)
When userspace turns on gmem_in_place_conversion while creating guest_memfd
without the MMAP flag, the absence of src_page should still be treated as an
error.
Additionally, to properly enable in-place copying for the TDX initial memory
region, userspace must not only specify source_addr to NULL, but also follow
a specific sequence (where steps 1/2/3/7 are required only for in-place copy):
1. create guest_memfd with MMAP flag
2. mmap the guest_memfd.
3. convert the initial memory range to shared.
4. copy initial content to the source page.
5. convert the initial memory range to private
6. invoke ioctl KVM_TDX_INIT_MEM_REGION.
7. do not unmap the source backend.
So, would it be reasonable to introduce a dedicated flag that allows userspace
to explicitly opt into the in-place copy functionality? e.g.,
diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
index 1585ec804066..d047a6efc728 100644
--- a/arch/x86/include/uapi/asm/kvm.h
+++ b/arch/x86/include/uapi/asm/kvm.h
@@ -1043,6 +1043,9 @@ struct kvm_tdx_init_vm {
};
#define KVM_TDX_MEASURE_MEMORY_REGION _BITULL(0)
+#define KVM_TDX_IN_PLACE_COPY_INITIAL_MEMORY_REGION _BITULL(1)
+#define KVM_TDX_INIT_MEM_VALID_FLAGS (KVM_TDX_MEASURE_MEMORY_REGION | \
+
KVM_TDX_IN_PLACE_COPY_INITIAL_MEMORY_REGION)
struct kvm_tdx_init_mem_region {
__u64 source_addr;
diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index 56d10333c61a..6072b38ceb37 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -3190,6 +3190,7 @@ static int tdx_gmem_post_populate(struct kvm *kvm, gfn_t
gfn, kvm_pfn_t pfn,
struct page *src_page, void *_arg)
{
struct tdx_gmem_post_populate_arg *arg = _arg;
+ bool in_place_copy = arg->flags &
KVM_TDX_IN_PLACE_COPY_INITIAL_MEMORY_REGION;
struct kvm_tdx *kvm_tdx = to_kvm_tdx(kvm);
u64 err, entry, level_state;
gpa_t gpa = gfn_to_gpa(gfn);
@@ -3199,7 +3200,7 @@ static int tdx_gmem_post_populate(struct kvm *kvm, gfn_t
gfn, kvm_pfn_t pfn,
return -EIO;
if (!src_page) {
- if (!gmem_in_place_conversion)
+ if (!in_place_copy)
return -EOPNOTSUPP;
src_page = pfn_to_page(pfn);
@@ -3245,7 +3246,7 @@ static int tdx_vcpu_init_mem_region(struct kvm_vcpu
*vcpu, struct kvm_tdx_cmd *c
if (kvm_tdx->state == TD_STATE_RUNNABLE)
return -EINVAL;
- if (cmd->flags & ~KVM_TDX_MEASURE_MEMORY_REGION)
+ if (cmd->flags & ~KVM_TDX_INIT_MEM_VALID_FLAGS)
return -EINVAL;
> + 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);
> @@ -3278,7 +3282,8 @@ static int tdx_vcpu_init_mem_region(struct kvm_vcpu
> *vcpu, struct kvm_tdx_cmd *c
> break;
> }
>
> - region.source_addr += PAGE_SIZE;
> + if (region.source_addr)
> + region.source_addr += PAGE_SIZE;
> region.gpa += PAGE_SIZE;
> region.nr_pages--;
>
>
> --
> 2.55.0.rc0.738.g0c8ab3ebcc-goog
>
>
