mshv: Align huge page stride with guest mapping

Ensure that a stride larger than 1 (huge page) is only used when page
points to a head of a huge page and both the guest frame number (gfn) and
the operation size (page_count) are aligned to the huge page size
(PTRS_PER_PMD). This matches the hypervisor requirement that map/unmap
operations for huge pages must be guest-aligned and cover a full huge page.

Add mshv_chunk_stride() to encapsulate this alignment and page-order
validation, and plumb a huge_page flag into the region chunk handlers.
This prevents issuing large-page map/unmap/share operations that the
hypervisor would reject due to misaligned guest mappings.

Fixes: abceb42 ("mshv: Fix huge page handling in memory region traversal")
Signed-off-by: Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>
Reviewed-by: Nuno Das Neves <nunodasneves@linux.microsoft.com>
Reviewed-by: Michael Kelley <mhklinux@outlook.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>

Author: Stanislav Kinsburskii

drivers/hv/mshv_regions.c

@@ -19,6 +19,41 @@
 
 #define MSHV_MAP_FAULT_IN_PAGES				PTRS_PER_PMD
 
+/**
+ * mshv_chunk_stride - Compute stride for mapping guest memory
+ * @page      : The page to check for huge page backing
+ * @gfn       : Guest frame number for the mapping
+ * @page_count: Total number of pages in the mapping
+ *
+ * Determines the appropriate stride (in pages) for mapping guest memory.
+ * Uses huge page stride if the backing page is huge and the guest mapping
+ * is properly aligned; otherwise falls back to single page stride.
+ *
+ * Return: Stride in pages, or -EINVAL if page order is unsupported.
+ */
+static int mshv_chunk_stride(struct page *page,
+			     u64 gfn, u64 page_count)
+{
+	unsigned int page_order;
+
+	/*
+	 * Use single page stride by default. For huge page stride, the
+	 * page must be compound and point to the head of the compound
+	 * page, and both gfn and page_count must be huge-page aligned.
+	 */
+	if (!PageCompound(page) || !PageHead(page) ||
+	    !IS_ALIGNED(gfn, PTRS_PER_PMD) ||
+	    !IS_ALIGNED(page_count, PTRS_PER_PMD))
+		return 1;
+
+	page_order = folio_order(page_folio(page));
+	/* The hypervisor only supports 2M huge page */
+	if (page_order != PMD_ORDER)
+		return -EINVAL;
+
+	return 1 << page_order;
+}
+
 /**
  * mshv_region_process_chunk - Processes a contiguous chunk of memory pages
  *                             in a region.
@@ -45,38 +80,37 @@ static long mshv_region_process_chunk(struct mshv_mem_region *region,
 				      int (*handler)(struct mshv_mem_region *region,
 						     u32 flags,
 						     u64 page_offset,
-						     u64 page_count))
+						     u64 page_count,
+						     bool huge_page))
 {
-	u64 count, stride;
-	unsigned int page_order;
+	u64 gfn = region->start_gfn + page_offset;
+	u64 count;
 	struct page *page;
-	int ret;
+	int stride, ret;
 
 	page = region->pages[page_offset];
 	if (!page)
 		return -EINVAL;
 
-	page_order = folio_order(page_folio(page));
-	/* The hypervisor only supports 4K and 2M page sizes */
-	if (page_order && page_order != PMD_ORDER)
-		return -EINVAL;
+	stride = mshv_chunk_stride(page, gfn, page_count);
+	if (stride < 0)
+		return stride;
 
-	stride = 1 << page_order;
-
-	/* Start at stride since the first page is validated */
+	/* Start at stride since the first stride is validated */
 	for (count = stride; count < page_count; count += stride) {
 		page = region->pages[page_offset + count];
 
 		/* Break if current page is not present */
 		if (!page)
 			break;
 
-		/* Break if page size changes */
-		if (page_order != folio_order(page_folio(page)))
+		/* Break if stride size changes */
+		if (stride != mshv_chunk_stride(page, gfn + count,
+						page_count - count))
 			break;
 	}
 
-	ret = handler(region, flags, page_offset, count);
+	ret = handler(region, flags, page_offset, count, stride > 1);
 	if (ret)
 		return ret;
 
@@ -108,7 +142,8 @@ static int mshv_region_process_range(struct mshv_mem_region *region,
 				     int (*handler)(struct mshv_mem_region *region,
 						    u32 flags,
 						    u64 page_offset,
-						    u64 page_count))
+						    u64 page_count,
+						    bool huge_page))
 {
 	long ret;
 
@@ -162,11 +197,10 @@ struct mshv_mem_region *mshv_region_create(u64 guest_pfn, u64 nr_pages,
 
 static int mshv_region_chunk_share(struct mshv_mem_region *region,
 				   u32 flags,
-				   u64 page_offset, u64 page_count)
+				   u64 page_offset, u64 page_count,
+				   bool huge_page)
 {
-	struct page *page = region->pages[page_offset];
-
-	if (PageHuge(page) || PageTransCompound(page))
+	if (huge_page)
 		flags |= HV_MODIFY_SPA_PAGE_HOST_ACCESS_LARGE_PAGE;
 
 	return hv_call_modify_spa_host_access(region->partition->pt_id,
@@ -188,11 +222,10 @@ int mshv_region_share(struct mshv_mem_region *region)
 
 static int mshv_region_chunk_unshare(struct mshv_mem_region *region,
 				     u32 flags,
-				     u64 page_offset, u64 page_count)
+				     u64 page_offset, u64 page_count,
+				     bool huge_page)
 {
-	struct page *page = region->pages[page_offset];
-
-	if (PageHuge(page) || PageTransCompound(page))
+	if (huge_page)
 		flags |= HV_MODIFY_SPA_PAGE_HOST_ACCESS_LARGE_PAGE;
 
 	return hv_call_modify_spa_host_access(region->partition->pt_id,
@@ -212,11 +245,10 @@ int mshv_region_unshare(struct mshv_mem_region *region)
 
 static int mshv_region_chunk_remap(struct mshv_mem_region *region,
 				   u32 flags,
-				   u64 page_offset, u64 page_count)
+				   u64 page_offset, u64 page_count,
+				   bool huge_page)
 {
-	struct page *page = region->pages[page_offset];
-
-	if (PageHuge(page) || PageTransCompound(page))
+	if (huge_page)
 		flags |= HV_MAP_GPA_LARGE_PAGE;
 
 	return hv_call_map_gpa_pages(region->partition->pt_id,
@@ -295,11 +327,10 @@ int mshv_region_pin(struct mshv_mem_region *region)
 
 static int mshv_region_chunk_unmap(struct mshv_mem_region *region,
 				   u32 flags,
-				   u64 page_offset, u64 page_count)
+				   u64 page_offset, u64 page_count,
+				   bool huge_page)
 {
-	struct page *page = region->pages[page_offset];
-
-	if (PageHuge(page) || PageTransCompound(page))
+	if (huge_page)
 		flags |= HV_UNMAP_GPA_LARGE_PAGE;
 
 	return hv_call_unmap_gpa_pages(region->partition->pt_id,