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Message-ID: <3f48795c0c34f4faf661394e5ad9805f9014ae23.1747264138.git.ackerleytng@google.com>
Date: Wed, 14 May 2025 16:42:19 -0700
From: Ackerley Tng <ackerleytng@...gle.com>
To: kvm@...r.kernel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
x86@...nel.org, linux-fsdevel@...r.kernel.org
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Subject: [RFC PATCH v2 40/51] KVM: guest_memfd: Update kvm_gmem_mapping_order
to account for page status
kvm_gmem_mapping_order() should return the maximum mapping order for a
gfn if a page were to be faulted in for that gfn.
For inodes that support a custom allocator, the maximum mapping order
should be determined by the custom allocator in conjunction with
guest_memfd.
This patch updates kvm_gmem_mapping_order() to take into account that
for the guestmem_hugetlb custom allocator, pages are split if any page
in a huge page range is shared.
Change-Id: I5c061af6cefdcbd708a4334cd58edc340afcf44e
Signed-off-by: Ackerley Tng <ackerleytng@...gle.com>
---
virt/kvm/guest_memfd.c | 72 ++++++++++++++++++++++++++++++++++++------
1 file changed, 62 insertions(+), 10 deletions(-)
diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index 04b1513c2998..8b5fe1360e58 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -709,19 +709,27 @@ static int kvm_gmem_split_folio_in_filemap(struct inode *inode, struct folio *fo
return ret;
}
+static inline bool kvm_gmem_should_split_at_index(struct inode *inode,
+ pgoff_t index)
+{
+ pgoff_t index_floor;
+ size_t nr_pages;
+ void *priv;
+
+ priv = kvm_gmem_allocator_private(inode);
+ nr_pages = kvm_gmem_allocator_ops(inode)->nr_pages_in_folio(priv);
+ index_floor = round_down(index, nr_pages);
+
+ return kvm_gmem_has_some_shared(inode, index_floor, nr_pages);
+}
+
static inline int kvm_gmem_try_split_folio_in_filemap(struct inode *inode,
struct folio *folio)
{
- size_t to_nr_pages;
- void *priv;
-
if (!kvm_gmem_has_custom_allocator(inode))
return 0;
- priv = kvm_gmem_allocator_private(inode);
- to_nr_pages = kvm_gmem_allocator_ops(inode)->nr_pages_in_page(priv);
-
- if (kvm_gmem_has_some_shared(inode, folio->index, to_nr_pages))
+ if (kvm_gmem_should_split_at_index(inode, folio->index))
return kvm_gmem_split_folio_in_filemap(inode, folio);
return 0;
@@ -890,6 +898,12 @@ static long kvm_gmem_merge_truncate_indices(struct inode *inode, pgoff_t index,
#else
+static inline bool kvm_gmem_should_split_at_index(struct inode *inode,
+ pgoff_t index)
+{
+ return false;
+}
+
static inline int kvm_gmem_try_split_folio_in_filemap(struct inode *inode,
struct folio *folio)
{
@@ -1523,7 +1537,7 @@ static inline struct file *kvm_gmem_get_file(struct kvm_memory_slot *slot)
return get_file_active(&slot->gmem.file);
}
-static pgoff_t kvm_gmem_get_index(struct kvm_memory_slot *slot, gfn_t gfn)
+static pgoff_t kvm_gmem_get_index(const struct kvm_memory_slot *slot, gfn_t gfn)
{
return gfn - slot->base_gfn + slot->gmem.pgoff;
}
@@ -2256,14 +2270,52 @@ int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot,
EXPORT_SYMBOL_GPL(kvm_gmem_get_pfn);
/**
- * Returns the mapping order for this @gfn in @slot.
+ * kvm_gmem_mapping_order() - Get the mapping order for this @gfn in @slot.
+ *
+ * @slot: the memslot that gfn belongs to.
+ * @gfn: the gfn to look up mapping order for.
*
* This is equal to max_order that would be returned if kvm_gmem_get_pfn() were
* called now.
+ *
+ * Return: the mapping order for this @gfn in @slot.
*/
int kvm_gmem_mapping_order(const struct kvm_memory_slot *slot, gfn_t gfn)
{
- return 0;
+ struct inode *inode;
+ struct file *file;
+ int ret;
+
+ file = kvm_gmem_get_file((struct kvm_memory_slot *)slot);
+ if (!file)
+ return 0;
+
+ inode = file_inode(file);
+
+ ret = 0;
+ if (kvm_gmem_has_custom_allocator(inode)) {
+ bool should_split;
+ pgoff_t index;
+
+ index = kvm_gmem_get_index(slot, gfn);
+
+ filemap_invalidate_lock_shared(inode->i_mapping);
+ should_split = kvm_gmem_should_split_at_index(inode, index);
+ filemap_invalidate_unlock_shared(inode->i_mapping);
+
+ if (!should_split) {
+ size_t nr_pages;
+ void *priv;
+
+ priv = kvm_gmem_allocator_private(inode);
+ nr_pages = kvm_gmem_allocator_ops(inode)->nr_pages_in_folio(priv);
+
+ ret = ilog2(nr_pages);
+ }
+ }
+
+ fput(file);
+ return ret;
}
EXPORT_SYMBOL_GPL(kvm_gmem_mapping_order);
--
2.49.0.1045.g170613ef41-goog
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