[PATCH v2 12/20] xen/balloon: Don't rely on the page granularity is the same for Xen and Linux

[Julien Grall]

For ARM64 guests, Linux is able to support either 64K or 4K page
granularity. Although, the hypercall interface is always based on 4K
page granularity.

With 64K page granuliarty, a single page will be spread over multiple
Xen frame.

When a driver request/free a balloon page, the balloon driver will have
to split the Linux page in 4K chunk before asking Xen to add/remove the
frame from the guest.

Note that this can work on any page granularity assuming it's a multiple
of 4K.

Signed-off-by: Julien Grall <julien.grall@xxxxxxxxxx>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Cc: David Vrabel <david.vrabel@xxxxxxxxxx>
Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
---
    Changes in v2:
        - Use xen_apply_to_page to split a page in 4K chunk
        - It's not necessary to have a smaller frame list. Re-use
        PAGE_SIZE
        - Convert reserve_additional_memory to use XEN_... macro
---
 drivers/xen/balloon.c | 147 +++++++++++++++++++++++++++++++++++---------------
 1 file changed, 105 insertions(+), 42 deletions(-)

diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
index fd93369..19a72b1 100644
--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -230,6 +230,7 @@ static enum bp_state reserve_additional_memory(long credit)
 	nid = memory_add_physaddr_to_nid(hotplug_start_paddr);
 
 #ifdef CONFIG_XEN_HAVE_PVMMU
+	/* TODO */
         /*
          * add_memory() will build page tables for the new memory so
          * the p2m must contain invalid entries so the correct
@@ -242,8 +243,8 @@ static enum bp_state reserve_additional_memory(long credit)
 	if (!xen_feature(XENFEAT_auto_translated_physmap)) {
 		unsigned long pfn, i;
 
-		pfn = PFN_DOWN(hotplug_start_paddr);
-		for (i = 0; i < balloon_hotplug; i++) {
+		pfn = XEN_PFN_DOWN(hotplug_start_paddr);
+		for (i = 0; i < (balloon_hotplug * XEN_PFN_PER_PAGE); i++) {
 			if (!set_phys_to_machine(pfn + i, INVALID_P2M_ENTRY)) {
 				pr_warn("set_phys_to_machine() failed, no memory added\n");
 				return BP_ECANCELED;
@@ -323,10 +324,72 @@ static enum bp_state reserve_additional_memory(long credit)
 }
 #endif /* CONFIG_XEN_BALLOON_MEMORY_HOTPLUG */
 
+static int set_frame(struct page *page, unsigned long pfn, void *data)
+{
+	unsigned long *index = data;
+
+	frame_list[(*index)++] = pfn;
+
+	return 0;
+}
+
+#ifdef CONFIG_XEN_HAVE_PVMMU
+static int pvmmu_update_mapping(struct page *page, unsigned long pfn,
+				void *data)
+{
+	unsigned long *index = data;
+	xen_pfn_t frame = frame_list[*index];
+
+	set_phys_to_machine(pfn, frame);
+	/* Link back into the page tables if not highmem. */
+	if (!PageHighMem(page)) {
+		int ret;
+		ret = HYPERVISOR_update_va_mapping(
+				(unsigned long)__va(pfn << XEN_PAGE_SHIFT),
+				mfn_pte(frame, PAGE_KERNEL),
+				0);
+		BUG_ON(ret);
+	}
+
+	(*index)++;
+
+	return 0;
+}
+#endif
+
+static int balloon_remove_mapping(struct page *page, unsigned long pfn,
+				  void *data)
+{
+	unsigned long *index = data;
+
+	/* We expect the frame_list to contain the same pfn */
+	BUG_ON(pfn != frame_list[*index]);
+
+	frame_list[*index] = pfn_to_mfn(pfn);
+
+#ifdef CONFIG_XEN_HAVE_PVMMU
+	if (!xen_feature(XENFEAT_auto_translated_physmap)) {
+		if (!PageHighMem(page)) {
+			int ret;
+
+			ret = HYPERVISOR_update_va_mapping(
+					(unsigned long)__va(pfn << XEN_PAGE_SHIFT),
+					__pte_ma(0), 0);
+			BUG_ON(ret);
+		}
+		__set_phys_to_machine(pfn, INVALID_P2M_ENTRY);
+	}
+#endif
+
+	(*index)++;
+
+	return 0;
+}
+
 static enum bp_state increase_reservation(unsigned long nr_pages)
 {
 	int rc;
-	unsigned long  pfn, i;
+	unsigned long i, frame_idx;
 	struct page   *page;
 	struct xen_memory_reservation reservation = {
 		.address_bits = 0,
@@ -343,44 +406,43 @@ static enum bp_state increase_reservation(unsigned long nr_pages)
 	}
 #endif
 
-	if (nr_pages > ARRAY_SIZE(frame_list))
-		nr_pages = ARRAY_SIZE(frame_list);
+	if (nr_pages > (ARRAY_SIZE(frame_list) / XEN_PFN_PER_PAGE))
+		nr_pages = ARRAY_SIZE(frame_list) / XEN_PFN_PER_PAGE;
 
+	frame_idx = 0;
 	page = list_first_entry_or_null(&ballooned_pages, struct page, lru);
 	for (i = 0; i < nr_pages; i++) {
 		if (!page) {
 			nr_pages = i;
 			break;
 		}
-		frame_list[i] = page_to_pfn(page);
+
+		rc = xen_apply_to_page(page, set_frame, &frame_idx);
+
 		page = balloon_next_page(page);
 	}
 
 	set_xen_guest_handle(reservation.extent_start, frame_list);
-	reservation.nr_extents = nr_pages;
+	reservation.nr_extents = nr_pages * XEN_PFN_PER_PAGE;
 	rc = HYPERVISOR_memory_op(XENMEM_populate_physmap, &reservation);
 	if (rc <= 0)
 		return BP_EAGAIN;
 
-	for (i = 0; i < rc; i++) {
+	/* rc is equal to the number of Xen page populated */
+	nr_pages = rc / XEN_PFN_PER_PAGE;
+
+	for (i = 0; i < nr_pages; i++) {
 		page = balloon_retrieve(false);
 		BUG_ON(page == NULL);
 
-		pfn = page_to_pfn(page);
-
 #ifdef CONFIG_XEN_HAVE_PVMMU
+		frame_idx = 0;
 		if (!xen_feature(XENFEAT_auto_translated_physmap)) {
-			set_phys_to_machine(pfn, frame_list[i]);
-
-			/* Link back into the page tables if not highmem. */
-			if (!PageHighMem(page)) {
-				int ret;
-				ret = HYPERVISOR_update_va_mapping(
-						(unsigned long)__va(pfn << PAGE_SHIFT),
-						mfn_pte(frame_list[i], PAGE_KERNEL),
-						0);
-				BUG_ON(ret);
-			}
+			int ret;
+
+			ret = xen_apply_to_page(page, pvmmu_update_mapping,
+						&frame_idx);
+			BUG_ON(ret);
 		}
 #endif
 
@@ -388,7 +450,7 @@ static enum bp_state increase_reservation(unsigned long nr_pages)
 		__free_reserved_page(page);
 	}
 
-	balloon_stats.current_pages += rc;
+	balloon_stats.current_pages += nr_pages;
 
 	return BP_DONE;
 }
@@ -396,7 +458,7 @@ static enum bp_state increase_reservation(unsigned long nr_pages)
 static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
 {
 	enum bp_state state = BP_DONE;
-	unsigned long  pfn, i;
+	unsigned long  pfn, i, frame_idx, nr_frames;
 	struct page   *page;
 	int ret;
 	struct xen_memory_reservation reservation = {
@@ -414,9 +476,10 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
 	}
 #endif
 
-	if (nr_pages > ARRAY_SIZE(frame_list))
-		nr_pages = ARRAY_SIZE(frame_list);
+	if (nr_pages > (ARRAY_SIZE(frame_list) / XEN_PFN_PER_PAGE))
+		nr_pages = ARRAY_SIZE(frame_list) / XEN_PFN_PER_PAGE;
 
+	frame_idx = 0;
 	for (i = 0; i < nr_pages; i++) {
 		page = alloc_page(gfp);
 		if (page == NULL) {
@@ -426,9 +489,12 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
 		}
 		scrub_page(page);
 
-		frame_list[i] = page_to_pfn(page);
+		ret = xen_apply_to_page(page, set_frame, &frame_idx);
+		BUG_ON(ret);
 	}
 
+	nr_frames = nr_pages * XEN_PFN_PER_PAGE;
+
 	/*
 	 * Ensure that ballooned highmem pages don't have kmaps.
 	 *
@@ -439,22 +505,19 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
 	kmap_flush_unused();
 
 	/* Update direct mapping, invalidate P2M, and add to balloon. */
+	frame_idx = 0;
 	for (i = 0; i < nr_pages; i++) {
-		pfn = frame_list[i];
-		frame_list[i] = pfn_to_mfn(pfn);
-		page = pfn_to_page(pfn);
+		/*
+		 * The Xen PFN for a given Linux Page are contiguous in
+		 * frame_list
+		 */
+		pfn = frame_list[frame_idx];
+		page = xen_pfn_to_page(pfn);
 
-#ifdef CONFIG_XEN_HAVE_PVMMU
-		if (!xen_feature(XENFEAT_auto_translated_physmap)) {
-			if (!PageHighMem(page)) {
-				ret = HYPERVISOR_update_va_mapping(
-						(unsigned long)__va(pfn << PAGE_SHIFT),
-						__pte_ma(0), 0);
-				BUG_ON(ret);
-			}
-			__set_phys_to_machine(pfn, INVALID_P2M_ENTRY);
-		}
-#endif
+
+		ret = xen_apply_to_page(page, balloon_remove_mapping,
+					&frame_idx);
+		BUG_ON(ret);
 
 		balloon_append(page);
 	}
@@ -462,9 +525,9 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
 	flush_tlb_all();
 
 	set_xen_guest_handle(reservation.extent_start, frame_list);
-	reservation.nr_extents   = nr_pages;
+	reservation.nr_extents   = nr_frames;
 	ret = HYPERVISOR_memory_op(XENMEM_decrease_reservation, &reservation);
-	BUG_ON(ret != nr_pages);
+	BUG_ON(ret != nr_frames);
 
 	balloon_stats.current_pages -= nr_pages;
 
-- 
2.1.4

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