On 8/8/2026 5:52 AM, Ackerley Tng via B4 Relay wrote: > From: Ackerley Tng <[email protected]> > > Update tdx_gmem_post_populate() to handle cases where userspace requests > "no source page". To handle "no source page", populate (perform > TDH.MEM.PAGE.ADD) using memory in-place at the target PFN. > > Allow "no source page" only when gmem_in_place_conversion is enabled, > because retroactively adding support for out-of-place conversion would mean > requiring a userspace update for a feature that's being deprecated. > > Also, KVM supporting "no source page" without in-place conversion would > effectively be an obscure zero-page optimization that relies on the page > being zeroed when it is allocated by guest_memfd. > > Rejecting "no source page" without in-place conversion scenario is valuable > for KVM developers since it helps newcomers understand what exactly is and > isn't possible. > > Signed-off-by: Sean Christopherson <[email protected]>
Nit: Is Sean's SoB intentional here? > Tested-by: Shivank Garg <[email protected]> > Signed-off-by: Ackerley Tng <[email protected]> Reviewed-by:Binbin Wu <[email protected]> > --- > Documentation/virt/kvm/x86/intel-tdx.rst | 4 ++++ > arch/x86/kvm/vmx/tdx.c | 8 +++++--- > 2 files changed, 9 insertions(+), 3 deletions(-) > > diff --git a/Documentation/virt/kvm/x86/intel-tdx.rst > b/Documentation/virt/kvm/x86/intel-tdx.rst > index 6a222e9d09541..d8d9409120e61 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 0 for @source_addr > +to represent "no source page". A source page is required if in-place > +conversion is not enabled or not supported. > + > 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 b272c20586a74..7654a9f5fa128 100644 > --- a/arch/x86/kvm/vmx/tdx.c > +++ b/arch/x86/kvm/vmx/tdx.c > @@ -3189,7 +3189,7 @@ 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; > > - kvm_tdx->page_add_src = src_page; > + kvm_tdx->page_add_src = src_page ?: pfn_to_page(pfn); > ret = kvm_tdp_mmu_map_private_pfn(arg->vcpu, gfn, pfn); > kvm_tdx->page_add_src = NULL; > > @@ -3235,7 +3235,8 @@ static int tdx_vcpu_init_mem_region(struct kvm_vcpu > *vcpu, struct kvm_tdx_cmd *c > if (copy_from_user(®ion, u64_to_user_ptr(cmd->data), sizeof(region))) > return -EFAULT; > > - if (!PAGE_ALIGNED(region.source_addr) || !region.source_addr || > + if (!PAGE_ALIGNED(region.source_addr) || > + (!gmem_in_place_conversion && !region.source_addr) || > !PAGE_ALIGNED(region.gpa) || !region.nr_pages || > region.gpa + (region.nr_pages << PAGE_SHIFT) <= region.gpa || > !vt_is_tdx_private_gpa(kvm, region.gpa) || > @@ -3266,7 +3267,8 @@ 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--; > >
