Merge tag 'vfio-v6.18-rc1-pt2' of https://github.com/awilliam/linux-vfio

Pull more VFIO updates from Alex Williamson:

 - Optimizations for DMA map and unmap opertions through the type1 vfio
   IOMMU backend.

   This uses various means of batching and hints from the mm structures
   to improve efficiency and therefore performance, resulting in a
   significant speedup for huge page use cases (Li Zhe)

 - Expose supported device migration features through debugfs (Cédric Le
   Goater)

* tag 'vfio-v6.18-rc1-pt2' of https://github.com/awilliam/linux-vfio:
  vfio: Dump migration features under debugfs
  vfio/type1: optimize vfio_unpin_pages_remote()
  vfio/type1: introduce a new member has_rsvd for struct vfio_dma
  vfio/type1: batch vfio_find_vpfn() in function vfio_unpin_pages_remote()
  vfio/type1: optimize vfio_pin_pages_remote()
  mm: introduce num_pages_contiguous()

2 files changed, 42 insertions, 1 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 06978b4dbeb8..f092ce3530bb 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1833,7 +1833,12 @@ static inline unsigned long memdesc_section(memdesc_flags_t mdf)
 {
 	return (mdf.f >> SECTIONS_PGSHIFT) & SECTIONS_MASK;
 }
-#endif
+#else /* !SECTION_IN_PAGE_FLAGS */
+static inline unsigned long memdesc_section(memdesc_flags_t mdf)
+{
+	return 0;
+}
+#endif /* SECTION_IN_PAGE_FLAGS */
 
 /**
  * folio_pfn - Return the Page Frame Number of a folio.
diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h
index d6c1011b38f2..f6a2b2d20016 100644
--- a/include/linux/mm_inline.h
+++ b/include/linux/mm_inline.h
@@ -617,4 +617,40 @@ static inline bool vma_has_recency(const struct vm_area_struct *vma)
 	return true;
 }
 
+/**
+ * num_pages_contiguous() - determine the number of contiguous pages
+ *			    that represent contiguous PFNs
+ * @pages: an array of page pointers
+ * @nr_pages: length of the array, at least 1
+ *
+ * Determine the number of contiguous pages that represent contiguous PFNs
+ * in @pages, starting from the first page.
+ *
+ * In some kernel configs contiguous PFNs will not have contiguous struct
+ * pages. In these configurations num_pages_contiguous() will return a num
+ * smaller than ideal number. The caller should continue to check for pfn
+ * contiguity after each call to num_pages_contiguous().
+ *
+ * Returns the number of contiguous pages.
+ */
+static inline size_t num_pages_contiguous(struct page **pages, size_t nr_pages)
+{
+	struct page *cur_page = pages[0];
+	unsigned long section = memdesc_section(cur_page->flags);
+	size_t i;
+
+	for (i = 1; i < nr_pages; i++) {
+		if (++cur_page != pages[i])
+			break;
+		/*
+		 * In unproblematic kernel configs, page_to_section() == 0 and
+		 * the whole check will get optimized out.
+		 */
+		if (memdesc_section(cur_page->flags) != section)
+			break;
+	}
+
+	return i;
+}
+
 #endif