Since guest_memfd now supports mmap(), folios have to be prepared before they are faulted into userspace.
When memory attributes are switched between shared and private, the up-to-date flags will be cleared.
Use the folio's up-to-date flag to indicate being ready for the guest usage and can be used to mark whether the folio is ready for shared OR private use.
Signed-off-by: Ackerley Tng ackerleytng@google.com
--- virt/kvm/guest_memfd.c | 131 ++++++++++++++++++++++++++++++++++++++++- virt/kvm/kvm_main.c | 2 + virt/kvm/kvm_mm.h | 7 +++ 3 files changed, 139 insertions(+), 1 deletion(-)
diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c index 110c4bbb004b..fb292e542381 100644 --- a/virt/kvm/guest_memfd.c +++ b/virt/kvm/guest_memfd.c @@ -129,13 +129,29 @@ static int __kvm_gmem_prepare_folio(struct kvm *kvm, struct kvm_memory_slot *slo }
/** - * Use the uptodate flag to indicate that the folio is prepared for KVM's usage. + * Use folio's up-to-date flag to indicate that this folio is prepared for usage + * by the guest. + * + * This flag can be used whether the folio is prepared for PRIVATE or SHARED + * usage. */ static inline void kvm_gmem_mark_prepared(struct folio *folio) { folio_mark_uptodate(folio); }
+/** + * Use folio's up-to-date flag to indicate that this folio is not yet prepared for + * usage by the guest. + * + * This flag can be used whether the folio is prepared for PRIVATE or SHARED + * usage. + */ +static inline void kvm_gmem_clear_prepared(struct folio *folio) +{ + folio_clear_uptodate(folio); +} + /* * Process @folio, which contains @gfn, so that the guest can use it. * The folio must be locked and the gfn must be contained in @slot. @@ -148,6 +164,12 @@ static int kvm_gmem_prepare_folio(struct kvm *kvm, struct kvm_memory_slot *slot, pgoff_t index; int r;
+ /* + * Defensively zero folio to avoid leaking kernel memory in + * uninitialized pages. This is important since pages can now be mapped + * into userspace, where hardware (e.g. TDX) won't be clearing those + * pages. + */ if (folio_test_hugetlb(folio)) { folio_zero_user(folio, folio->index << PAGE_SHIFT); } else { @@ -1017,6 +1039,7 @@ static vm_fault_t kvm_gmem_fault(struct vm_fault *vmf) { struct inode *inode; struct folio *folio; + bool is_prepared;
inode = file_inode(vmf->vma->vm_file); if (!kvm_gmem_is_faultable(inode, vmf->pgoff)) @@ -1026,6 +1049,31 @@ static vm_fault_t kvm_gmem_fault(struct vm_fault *vmf) if (!folio) return VM_FAULT_SIGBUS;
+ is_prepared = folio_test_uptodate(folio); + if (!is_prepared) { + unsigned long nr_pages; + unsigned long i; + + if (folio_test_hugetlb(folio)) { + folio_zero_user(folio, folio->index << PAGE_SHIFT); + } else { + /* + * Defensively zero folio to avoid leaking kernel memory in + * uninitialized pages. This is important since pages can now be + * mapped into userspace, where hardware (e.g. TDX) won't be + * clearing those pages. + * + * Will probably need a version of kvm_gmem_prepare_folio() to + * prepare the page for SHARED use. + */ + nr_pages = folio_nr_pages(folio); + for (i = 0; i < nr_pages; i++) + clear_highpage(folio_page(folio, i)); + } + + kvm_gmem_mark_prepared(folio); + } + vmf->page = folio_file_page(folio, vmf->pgoff); return VM_FAULT_LOCKED; } @@ -1593,6 +1641,87 @@ long kvm_gmem_populate(struct kvm *kvm, gfn_t start_gfn, void __user *src, long } EXPORT_SYMBOL_GPL(kvm_gmem_populate);
+static void kvm_gmem_clear_prepared_range(struct inode *inode, pgoff_t start, + pgoff_t end) +{ + pgoff_t index; + + filemap_invalidate_lock_shared(inode->i_mapping); + + /* TODO: replace iteration with filemap_get_folios() for efficiency. */ + for (index = start; index < end;) { + struct folio *folio; + + /* Don't use kvm_gmem_get_folio to avoid allocating */ + folio = filemap_lock_folio(inode->i_mapping, index); + if (IS_ERR(folio)) { + ++index; + continue; + } + + kvm_gmem_clear_prepared(folio); + + index = folio_next_index(folio); + folio_unlock(folio); + folio_put(folio); + } + + filemap_invalidate_unlock_shared(inode->i_mapping); +} + +/** + * Clear the prepared flag for all folios in gfn range [@start, @end) in memslot + * @slot. + */ +static void kvm_gmem_clear_prepared_slot(struct kvm_memory_slot *slot, gfn_t start, + gfn_t end) +{ + pgoff_t start_offset; + pgoff_t end_offset; + struct file *file; + + file = kvm_gmem_get_file(slot); + if (!file) + return; + + start_offset = start - slot->base_gfn + slot->gmem.pgoff; + end_offset = end - slot->base_gfn + slot->gmem.pgoff; + + kvm_gmem_clear_prepared_range(file_inode(file), start_offset, end_offset); + + fput(file); +} + +/** + * Clear the prepared flag for all folios for any slot in gfn range + * [@start, @end) in @kvm. + */ +void kvm_gmem_clear_prepared_vm(struct kvm *kvm, gfn_t start, gfn_t end) +{ + int i; + + lockdep_assert_held(&kvm->slots_lock); + + for (i = 0; i < kvm_arch_nr_memslot_as_ids(kvm); i++) { + struct kvm_memslot_iter iter; + struct kvm_memslots *slots; + + slots = __kvm_memslots(kvm, i); + kvm_for_each_memslot_in_gfn_range(&iter, slots, start, end) { + struct kvm_memory_slot *slot; + gfn_t gfn_start; + gfn_t gfn_end; + + slot = iter.slot; + gfn_start = max(start, slot->base_gfn); + gfn_end = min(end, slot->base_gfn + slot->npages); + + if (iter.slot->flags & KVM_MEM_GUEST_MEMFD) + kvm_gmem_clear_prepared_slot(iter.slot, gfn_start, gfn_end); + } + } +} + /** * Returns true if pages in range [@start, @end) in inode @inode have no * userspace mappings. diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 1a7bbcc31b7e..255d27df7f5c 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -2565,6 +2565,8 @@ static int kvm_vm_set_mem_attributes(struct kvm *kvm, gfn_t start, gfn_t end, KVM_BUG_ON(r, kvm); }
+ kvm_gmem_clear_prepared_vm(kvm, start, end); + kvm_handle_gfn_range(kvm, &post_set_range);
out_unlock: diff --git a/virt/kvm/kvm_mm.h b/virt/kvm/kvm_mm.h index d8ff2b380d0e..25fd0d9f66cc 100644 --- a/virt/kvm/kvm_mm.h +++ b/virt/kvm/kvm_mm.h @@ -43,6 +43,7 @@ int kvm_gmem_bind(struct kvm *kvm, struct kvm_memory_slot *slot, void kvm_gmem_unbind(struct kvm_memory_slot *slot); int kvm_gmem_should_set_attributes(struct kvm *kvm, gfn_t start, gfn_t end, unsigned long attrs); +void kvm_gmem_clear_prepared_vm(struct kvm *kvm, gfn_t start, gfn_t end); #else static inline void kvm_gmem_init(struct module *module) { @@ -68,6 +69,12 @@ static inline int kvm_gmem_should_set_attributes(struct kvm *kvm, gfn_t start, return 0; }
+static inline void kvm_gmem_clear_prepared_slots(struct kvm *kvm, + gfn_t start, gfn_t end) +{ + WARN_ON_ONCE(1); +} + #endif /* CONFIG_KVM_PRIVATE_MEM */
#endif /* __KVM_MM_H__ */