[PATCH v8 16/46] KVM: guest_memfd: Return early if range already has requested attributes
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: Ackerley Tng <redacted> Extract a helper out of kvm_gmem_range_is_private() that checks that a range has given attributes. Optimize setting memory attributes by returning early if all pages in the requested range already has the requested attributes. Reviewed-by: Fuad Tabba <redacted> Signed-off-by: Ackerley Tng <redacted> --- virt/kvm/guest_memfd.c | 31 +++++++++++++++++++++++-------- 1 file changed, 23 insertions(+), 8 deletions(-)
diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index 3c94442bc8131..cec8fa26ece17 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c@@ -86,6 +86,23 @@ static bool kvm_gmem_is_shared_mem(struct inode *inode, pgoff_t index) return !kvm_gmem_is_private_mem(inode, index); } +static bool kvm_gmem_range_has_attributes(struct maple_tree *mt, + pgoff_t index, size_t nr_pages, + u64 attributes) +{ + pgoff_t end = index + nr_pages - 1; + void *entry; + + lockdep_assert(mt_lock_is_held(mt)); + + mt_for_each(mt, entry, index, end) { + if (xa_to_value(entry) != attributes) + return false; + } + + return true; +} + static int __kvm_gmem_prepare_folio(struct kvm *kvm, struct kvm_memory_slot *slot, pgoff_t index, struct folio *folio) {
@@ -653,12 +670,15 @@ static int __kvm_gmem_set_attributes(struct inode *inode, pgoff_t start, pgoff_t end = start + nr_pages; struct maple_tree *mt; struct ma_state mas; - int r; + int r = 0; mt = &gi->attributes; filemap_invalidate_lock(mapping); + if (kvm_gmem_range_has_attributes(mt, start, nr_pages, attrs)) + goto out; + mas_init(&mas, mt, start); r = kvm_gmem_mas_preallocate(&mas, attrs, start, nr_pages); if (r) {
@@ -1148,19 +1168,14 @@ 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; + return kvm_gmem_range_has_attributes(mt, index, nr_pages, + KVM_MEMORY_ATTRIBUTE_PRIVATE); } static long __kvm_gmem_populate(struct kvm *kvm, struct kvm_memory_slot *slot,
--
2.55.0.rc0.738.g0c8ab3ebcc-goog