Re: [PATCH v8 23/46] KVM: TDX: Make source page optional for KVM_TDX_INIT_MEM_REGION
From: Yan Zhao <hidden>
Date: 2026-06-22 07:38:06
Also in:
kvm, linux-coco, linux-doc, linux-kselftest, linux-mm, lkml
Subsystem:
kernel virtual machine for x86 (kvm/x86), the rest, x86 architecture (32-bit and 64-bit) · Maintainers:
Sean Christopherson, Paolo Bonzini, Linus Torvalds, Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen
On Thu, Jun 18, 2026 at 05:32:00PM -0700, Ackerley Tng via B4 Relay wrote:
quoted hunk ↗ jump to hunk
From: Ackerley Tng <redacted> 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 <redacted> Signed-off-by: Sean Christopherson <seanjc@google.com> --- 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;
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+ 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