On Mon, Jun 22, 2026, Yan Zhao wrote: > 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.
Why MMAP? Shouldn't this be a general "if (!src_page && !up-to-date)"? Just because userspace _can_ mmap() the memory doesn't mean userspace _has_ mmap()'d and written memory. And when write() lands, MMAP wouldn't be necessary to initialize the memory. > 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., Why? It's userspace's responsibility to get the above right. If userspace fails to provide a src_page when it doesn't want in-place copy, that's a userspace bug.
