--- /dev/null
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/errno.h>
+#include <linux/gfp.h>
+#include <linux/kernel.h>
+#include <linux/mm.h>
+#include <linux/memremap.h>
+#include <linux/slab.h>
+
+#include <asm/page.h>
+
+#include <xen/page.h>
+#include <xen/xen.h>
+
+static DEFINE_MUTEX(list_lock);
+static LIST_HEAD(page_list);
+static unsigned int list_count;
+
+static int fill_list(unsigned int nr_pages)
+{
+ struct dev_pagemap *pgmap;
+ void *vaddr;
+ unsigned int i, alloc_pages = round_up(nr_pages, PAGES_PER_SECTION);
+ int ret;
+
+ pgmap = kzalloc(sizeof(*pgmap), GFP_KERNEL);
+ if (!pgmap)
+ return -ENOMEM;
+
+ pgmap->type = MEMORY_DEVICE_GENERIC;
+ pgmap->res.name = "Xen scratch";
+ pgmap->res.flags = IORESOURCE_MEM | IORESOURCE_BUSY;
+
+ ret = allocate_resource(&iomem_resource, &pgmap->res,
+ alloc_pages * PAGE_SIZE, 0, -1,
+ PAGES_PER_SECTION * PAGE_SIZE, NULL, NULL);
+ if (ret < 0) {
+ pr_err("Cannot allocate new IOMEM resource\n");
+ kfree(pgmap);
+ return ret;
+ }
+
+#ifdef CONFIG_XEN_HAVE_PVMMU
+ /*
+ * memremap will build page tables for the new memory so
+ * the p2m must contain invalid entries so the correct
+ * non-present PTEs will be written.
+ *
+ * If a failure occurs, the original (identity) p2m entries
+ * are not restored since this region is now known not to
+ * conflict with any devices.
+ */
+ if (!xen_feature(XENFEAT_auto_translated_physmap)) {
+ xen_pfn_t pfn = PFN_DOWN(pgmap->res.start);
+
+ for (i = 0; i < alloc_pages; i++) {
+ if (!set_phys_to_machine(pfn + i, INVALID_P2M_ENTRY)) {
+ pr_warn("set_phys_to_machine() failed, no memory added\n");
+ release_resource(&pgmap->res);
+ kfree(pgmap);
+ return -ENOMEM;
+ }
+ }
+ }
+#endif
+
+ vaddr = memremap_pages(pgmap, NUMA_NO_NODE);
+ if (IS_ERR(vaddr)) {
+ pr_err("Cannot remap memory range\n");
+ release_resource(&pgmap->res);
+ kfree(pgmap);
+ return PTR_ERR(vaddr);
+ }
+
+ for (i = 0; i < alloc_pages; i++) {
+ struct page *pg = virt_to_page(vaddr + PAGE_SIZE * i);
+
+ BUG_ON(!virt_addr_valid(vaddr + PAGE_SIZE * i));
+ list_add(&pg->lru, &page_list);
+ list_count++;
+ }
+
+ return 0;
+}
+
+/**
+ * xen_alloc_unpopulated_pages - alloc unpopulated pages
+ * @nr_pages: Number of pages
+ * @pages: pages returned
+ * @return 0 on success, error otherwise
+ */
+int xen_alloc_unpopulated_pages(unsigned int nr_pages, struct page **pages)
+{
+ unsigned int i;
+ int ret = 0;
+
+ mutex_lock(&list_lock);
+ if (list_count < nr_pages) {
+ ret = fill_list(nr_pages - list_count);
+ if (ret)
+ goto out;
+ }
+
+ for (i = 0; i < nr_pages; i++) {
+ struct page *pg = list_first_entry_or_null(&page_list,
+ struct page,
+ lru);
+
+ BUG_ON(!pg);
+ list_del(&pg->lru);
+ list_count--;
+ pages[i] = pg;
+
+#ifdef CONFIG_XEN_HAVE_PVMMU
+ if (!xen_feature(XENFEAT_auto_translated_physmap)) {
+ ret = xen_alloc_p2m_entry(page_to_pfn(pg));
+ if (ret < 0) {
+ unsigned int j;
+
+ for (j = 0; j <= i; j++) {
+ list_add(&pages[j]->lru, &page_list);
+ list_count++;
+ }
+ goto out;
+ }
+ }
+#endif
+ }
+
+out:
+ mutex_unlock(&list_lock);
+ return ret;
+}
+EXPORT_SYMBOL(xen_alloc_unpopulated_pages);
+
+/**
+ * xen_free_unpopulated_pages - return unpopulated pages
+ * @nr_pages: Number of pages
+ * @pages: pages to return
+ */
+void xen_free_unpopulated_pages(unsigned int nr_pages, struct page **pages)
+{
+ unsigned int i;
+
+ mutex_lock(&list_lock);
+ for (i = 0; i < nr_pages; i++) {
+ list_add(&pages[i]->lru, &page_list);
+ list_count++;
+ }
+ mutex_unlock(&list_lock);
+}
+EXPORT_SYMBOL(xen_free_unpopulated_pages);
+
+#ifdef CONFIG_XEN_PV
+static int __init init(void)
+{
+ unsigned int i;
+
+ if (!xen_domain())
+ return -ENODEV;
+
+ if (!xen_pv_domain())
+ return 0;
+
+ /*
+ * Initialize with pages from the extra memory regions (see
+ * arch/x86/xen/setup.c).
+ */
+ for (i = 0; i < XEN_EXTRA_MEM_MAX_REGIONS; i++) {
+ unsigned int j;
+
+ for (j = 0; j < xen_extra_mem[i].n_pfns; j++) {
+ struct page *pg =
+ pfn_to_page(xen_extra_mem[i].start_pfn + j);
+
+ list_add(&pg->lru, &page_list);
+ list_count++;
+ }
+ }
+
+ return 0;
+}
+subsys_initcall(init);
+#endif
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