guest_memfd就地转换 · v12

引入kvm_arch_has_gmem_convert()宏来守卫guest_memfd调用arch转换钩子，x86只有一半需要运行时钩子，通过死代码消除去掉空调开销，并提供kvm_arch_gmem_make_private声明。

在kvm_gmem_populate()中用kvm_mem_is_private()替代等价的open-coded判断，简化当前逻辑并可避免将来提供range-based gmem查找API。

为guest_memfd引入maple树跟踪每inode的private/shared属性，用filemap_invalidate_lock保护；在kvm_gmem_get_pfn中先释放folio引用再解锁，避免转换请求看到陈旧高refcount。

将KVM_GENERIC_MEMORY_ATTRIBUTES Kconfig改名为KVM_VM_MEMORY_ATTRIBUTES，明确其per-VM属性语义，为后续引入guest_memfd独立内存属性追踪做准备，无功能变化。

报告KVM_MEMORY_ATTRIBUTE_PRIVATE支持改为仅当kvm_arch_has_private_mem宏定义时，去除与CONFIG_KVM_VM_MEMORY_ATTRIBUTES的耦合，防止arm64在系统范围检查时误报PRIVATE支持。

将内存属性API重命名加入vm_前缀，如kvm_vm_set_mem_attributes()改为kvm_set_vm_mem_attributes()，以区分未来guest_memfd自身的属性来源，trace函数同步更新。

把kvm_mem_is_private()改名为kvm_is_private_gfn()，为将来kvm_vm_is_private_gfn()和kvm_gmem_is_private_gfn()两个查询函数提供一致的命名前缀。

用static call提供通用kvm_is_private_gfn()接口，运行时选择实现；现有基于VM属性的检查改名为kvm_vm_is_private_gfn()，为切换gmem查找做准备。

新增全局变量gmem_in_place_conversion用于启用in-place转换，并将__kvm_is_private_gfn() static call指向guest_memfd版本，后续会暴露为模块参数。

在kvm_host.h中整理private memory与guest_memfd相关#ifdeffery，把kvm_arch_has_private_mem() stub和相关函数声明移到已有条件编译块内，代码聚类无功能变化。

in-place转换启用时，从guest_memfd移除folio需同时invalidate SHARED和PRIVATE映射；但per-VM追踪模式下只能zap对应类型，否则PUNCH_HOLE会误伤VMA映射。

in-place转换启用时强制设置KVM_MEMSLOT_GMEM_ONLY，使guest_memfd成为shared和private内存唯一backing源，简化stage2失效；userspace_addr仍用于kvm_read_guest等但需用户保证一致。

让invalidation start helper接受mapping type filter参数，调用者可指定只失效shared、private或两者；下一步转换将只zap与目标状态不同的映射。

新增KVM_SET_MEMORY_ATTRIBUTES2 ioctl和struct，具备R/W语义，支持部分转换时记录失败offset，struct预留padding，并用KVM_CAP_GUEST_MEMFD_MEMORY_ATTRIBUTES宣传能力。

转换到private前检查folio refcount以确保无其他使用者；新增error_offset字段，安全检查失败返回-EAGAIN并复制偏移给用户，便于重试或处理。

PRIVATE到SHARED转换时立即调用arch make_shared回调以更新硬件元数据，避免按需更新；to-private不主动调用因为需要确切GFN且必须在fault时按需处理。

增加函数检查gmem范围是否已具备请求的属性，设置内存属性时若整个范围已满足则提前返回，避免无谓的转换和invalidation操作。

转换安全检查前调用lru_cache_drain_for_folio()排空lru_add和mlock fbatch可能附加的refcount，之后若refcount仍高则视为真正在用；folio_maybe_dma_pinned()作为DMA引用判断。

将folio初始化逻辑移到__kvm_gmem_get_pfn()，使kvm_gmem_populate()路径也能先清零页面，用uptodate标志保证只零一次，避免未初始化主机内存泄漏给guest。

SNP_LAUNCH_UPDATE在in-place转换启用时允许uaddr为NULL，让用户先mmap guest_memfd写shared内存再转换private；per-VM属性模式下仍强制非NULL源地址。

TDX的tdx_gmem_post_populate()支持无源页场景，直接在目标PFN上原地执行TDH.MEM.PAGE.ADD；仅当in-place转换启用时允许，否则拒绝以避免晦涩优化。

将KVM_VM_MEMORY_ATTRIBUTES Kconfig移到x86专属，因为per-VM属性追踪已被弃用，防止其他架构引入；公共代码保留在common KVM方便将来撤销。

新增Kconfig选项和条件模块参数，让用户可禁用per-VM属性并启用per-gmem in-place转换；模块加载后禁止动态切换以避免同一KVM实例混合两种追踪模式。

在x86 CoCo VM且启用in-place转换时，允许用户为guest_memfd指定INIT_SHARED标志，使实例初始化即为shared内存。

selftests添加memslot时先创建guest_memfd再创建普通backing fd，以便后续当guest_memfd支持mmap时可直接复用gmem fd作为唯一内存来源。

将selftests中guest_memfd相关变量和参数统一改名为gmem_fd/gmem_offset，去除冗长前缀，无功能变化。

vm_mem_add()支持传入gmem_flags创建guest_memfd并作为内存槽fd；mmap guest_memfd时使用gmem_offset且固定MAP_SHARED，新增kvm_slot_to_fd()辅助获取fd。

新增全局变量kvm_has_gmem_attributes表示guest_memfd自身跟踪内存属性而非VM级，并在selftests中同步到guest以避免host/guest状态不一致。

新增gmem_ioctl宏和gmem_set_memory_attributes()系列helpers，__变体返回错误码而非abort；抽取TEST_ASSERT_SUPPORTED_ATTRIBUTES宏供新旧属性设置函数复用。

新增guest_memfd单页转换selftest，验证默认private状态经private->shared->private的基本流程，并搭建可扩展的转换测试基础设施，测试限定x86。

在guest_memfd转换selftest中增加INIT_SHARED场景用例，验证内存初始为shared时private/shared转换仍能正确工作。

From: Ackerley Tng ackerleytng@google.com The existing guest_memfd conversion tests only use single-page memory regions. This provides no coverage for multi-page guest_memfd objects, specifically w

新增两个转换先于内存分配的测试用例，覆盖guest_memfd区域尚未分配时的两种转换方向，验证内核记录属性请求并在后续分配时应用。

From: Ackerley Tng ackerleytng@google.com Add a guest_memfd selftest to verify that memory conversions work correctly with allocated folios in different layouts. By iterating through which pages a

From: Ackerley Tng ackerleytng@google.com Add a test to verify that deallocating a page in a guest memfd region via fallocate() with FALLOC_FL_PUNCH_HOLE does not alter the shared or private status

From: Sean Christopherson seanjc@google.com Add a test to verify that a guest_memfd’s shared/private status is consistent across processes, and that any shared pages previously mapped in any proces

From: Ackerley Tng ackerleytng@google.com Add helper functions to allow KVM selftests to pin memory using CONFIG_GUP_TEST. This is useful for creating test scenarios where some page has an increase

From: Ackerley Tng ackerleytng@google.com Add a selftest to verify that converting a shared guest_memfd page to a private page fails if the page has an elevated reference count. When KVM converts

From: Ackerley Tng ackerleytng@google.com private_mem_conversions_test used to reset the shared memory that was used for the test to an initial pattern at the end of each test iteration. Then, it w

From: Ackerley Tng ackerleytng@google.com Introduce a new helper, kvm_gpa_to_guest_memfd(), to find the guest_memfd-related details of a memory region that contains a given guest physical address (

From: Sean Christopherson seanjc@google.com Introduce vm_mem_set_memory_attributes(), which handles setting of memory attributes for a range of guest physical addresses, regardless of whether the a

From: Ackerley Tng ackerleytng@google.com The TEST_EXPECT_SIGBUS macro is not thread-safe as it uses a global sigjmp_buf and installs a global SIGBUS signal handler. If multiple threads execute the

From: Ackerley Tng ackerleytng@google.com Currently, vm_mem_add derives the backing source page size, alignment padding, and mmap size from the backing source type upfront before checking if guest_

From: Ackerley Tng ackerleytng@google.com Update private_mem_conversions_test for in-place conversions. In-place conversions support is detected in selftests with kvm_has_gmem_attributes. With in-

From: Sean Christopherson seanjc@google.com Skip setting memory to private in the private memory exits test when using per-gmem memory attributes, as memory is initialized to private by default for