[PATCH v8 10/46] KVM: guest_memfd: Wire up core private/shared attribute interfaces
From: Ackerley Tng via B4 Relay <devnull+ackerleytng.google.com@kernel.org>
Date: 2026-06-19 00:31:48
Also in:
b4-sent, kvm, linux-coco, linux-doc, linux-kselftest, linux-mm, lkml
Subsystem:
kernel virtual machine (kvm), the rest · Maintainers:
Paolo Bonzini, Linus Torvalds
From: Sean Christopherson <seanjc@google.com> With in-place conversion, guest_memfd is able to track the private/shared status of memory. Use a global flag to toggle between tracking private/shared status per-vm or within guest_memfd. When queried for supported vm memory attributes, return 0 if attributes are tracked in guest_memfd. When querying for memory attributes over a range, look up memory attributes based on the flag's state at query time. For per-GFN memory attribute queries, choosing an implementation (VM or guest_memfd lookup) at KVM load time. The flag is always false for now and will be made toggle-able after all in-place conversion features are added in subsequent patches. If/since the flag is false, if CONFIG_KVM_VM_MEMORY_ATTRIBUTES is also not selected, the per-GFN memory attribute query defaults to returning 0 (false/not private). Co-developed-by: Ackerley Tng <redacted> Signed-off-by: Ackerley Tng <redacted> Signed-off-by: Sean Christopherson <seanjc@google.com> --- include/linux/kvm_host.h | 4 ++++ virt/kvm/guest_memfd.c | 22 +++++++++++++++++++--- virt/kvm/kvm_main.c | 12 +++++++++++- 3 files changed, 34 insertions(+), 4 deletions(-)
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 27687fb9d5201..acb552745b428 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h@@ -2560,6 +2560,8 @@ static inline bool kvm_mem_range_is_private(struct kvm *kvm, gfn_t start, #endif /* CONFIG_KVM_VM_MEMORY_ATTRIBUTES */ #ifdef kvm_arch_has_private_mem +extern bool gmem_in_place_conversion; + typedef bool (kvm_mem_is_private_t)(struct kvm *kvm, gfn_t gfn); DECLARE_STATIC_CALL(__kvm_mem_is_private, kvm_mem_is_private_t);
@@ -2568,6 +2570,8 @@ static inline bool kvm_mem_is_private(struct kvm *kvm, gfn_t gfn) return static_call(__kvm_mem_is_private)(kvm, gfn); } #else +#define gmem_in_place_conversion false + static inline bool kvm_mem_is_private(struct kvm *kvm, gfn_t gfn) { return false;
diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index bca912db5be6e..e0e544ef47d69 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c@@ -926,6 +926,24 @@ int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot, EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_gmem_get_pfn); #ifdef CONFIG_HAVE_KVM_ARCH_GMEM_POPULATE +static bool kvm_gmem_range_is_private(struct file *file, pgoff_t index, + size_t nr_pages, struct kvm *kvm, gfn_t gfn) +{ + struct maple_tree *mt = &GMEM_I(file_inode(file))->attributes; + pgoff_t end = index + nr_pages - 1; + void *entry; + + if (!gmem_in_place_conversion) + return kvm_range_has_vm_memory_attributes(kvm, gfn, gfn + nr_pages, + KVM_MEMORY_ATTRIBUTE_PRIVATE, + KVM_MEMORY_ATTRIBUTE_PRIVATE); + + mt_for_each(mt, entry, index, end) { + if (xa_to_value(entry) != KVM_MEMORY_ATTRIBUTE_PRIVATE) + return false; + } + return true; +} static long __kvm_gmem_populate(struct kvm *kvm, struct kvm_memory_slot *slot, struct file *file, gfn_t gfn, struct page *src_page,
@@ -946,9 +964,7 @@ static long __kvm_gmem_populate(struct kvm *kvm, struct kvm_memory_slot *slot, folio_unlock(folio); - if (!kvm_range_has_vm_memory_attributes(kvm, gfn, gfn + 1, - KVM_MEMORY_ATTRIBUTE_PRIVATE, - KVM_MEMORY_ATTRIBUTE_PRIVATE)) { + if (!kvm_gmem_range_is_private(file, index, 1, kvm, gfn)) { ret = -EINVAL; goto out_put_folio; }
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 8b238e461b854..01761f6e25d25 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c@@ -101,6 +101,10 @@ EXPORT_SYMBOL_FOR_KVM_INTERNAL(halt_poll_ns_shrink); static bool __ro_after_init allow_unsafe_mappings; module_param(allow_unsafe_mappings, bool, 0444); +#ifdef kvm_arch_has_private_mem +bool __ro_after_init gmem_in_place_conversion = false; +#endif + /* * Ordering of locks: *
@@ -2422,6 +2426,9 @@ static int kvm_vm_ioctl_clear_dirty_log(struct kvm *kvm, static u64 kvm_supported_vm_mem_attributes(struct kvm *kvm) { #ifdef kvm_arch_has_private_mem + if (gmem_in_place_conversion) + return 0; + if (!kvm || kvm_arch_has_private_mem(kvm)) return KVM_MEMORY_ATTRIBUTE_PRIVATE; #endif
@@ -2633,8 +2640,11 @@ EXPORT_STATIC_CALL_GPL(__kvm_mem_is_private); static void kvm_init_memory_attributes(void) { + if (gmem_in_place_conversion) + static_call_update(__kvm_mem_is_private, kvm_gmem_is_private); #ifdef CONFIG_KVM_VM_MEMORY_ATTRIBUTES - static_call_update(__kvm_mem_is_private, kvm_vm_mem_is_private); + else + static_call_update(__kvm_mem_is_private, kvm_vm_mem_is_private); #endif } #else
--
2.55.0.rc0.738.g0c8ab3ebcc-goog