--- zzzz-none-000/linux-3.10.107/arch/um/kernel/physmem.c	2017-06-27 09:49:32.000000000 +0000
+++ scorpion-7490-727/linux-3.10.107/arch/um/kernel/physmem.c	2021-02-04 17:41:59.000000000 +0000
@@ -8,6 +8,7 @@
 #include <linux/mm.h>
 #include <linux/pfn.h>
 #include <asm/page.h>
+#include <asm/sections.h>
 #include <as-layout.h>
 #include <init.h>
 #include <kern.h>
@@ -22,39 +23,19 @@
 
 extern unsigned long long physmem_size;
 
-int __init init_maps(unsigned long physmem, unsigned long iomem,
+void __init mem_total_pages(unsigned long physmem, unsigned long iomem,
 		     unsigned long highmem)
 {
-	struct page *p, *map;
-	unsigned long phys_len, phys_pages, highmem_len, highmem_pages;
-	unsigned long iomem_len, iomem_pages, total_len, total_pages;
-	int i;
-
-	phys_pages = physmem >> PAGE_SHIFT;
-	phys_len = phys_pages * sizeof(struct page);
-
-	iomem_pages = iomem >> PAGE_SHIFT;
-	iomem_len = iomem_pages * sizeof(struct page);
+	unsigned long phys_pages, highmem_pages;
+	unsigned long iomem_pages, total_pages;
 
+	phys_pages    = physmem >> PAGE_SHIFT;
+	iomem_pages   = iomem   >> PAGE_SHIFT;
 	highmem_pages = highmem >> PAGE_SHIFT;
-	highmem_len = highmem_pages * sizeof(struct page);
 
-	total_pages = phys_pages + iomem_pages + highmem_pages;
-	total_len = phys_len + iomem_len + highmem_len;
-
-	map = alloc_bootmem_low_pages(total_len);
-	if (map == NULL)
-		return -ENOMEM;
-
-	for (i = 0; i < total_pages; i++) {
-		p = &map[i];
-		memset(p, 0, sizeof(struct page));
-		SetPageReserved(p);
-		INIT_LIST_HEAD(&p->lru);
-	}
+	total_pages   = phys_pages + iomem_pages + highmem_pages;
 
 	max_mapnr = total_pages;
-	return 0;
 }
 
 void map_memory(unsigned long virt, unsigned long phys, unsigned long len,
@@ -75,24 +56,51 @@
 	}
 }
 
-extern int __syscall_stub_start;
-
+/**
+ * setup_physmem() - Setup physical memory for UML
+ * @start:	Start address of the physical kernel memory,
+ *		i.e start address of the executable image.
+ * @reserve_end:	end address of the physical kernel memory.
+ * @len:	Length of total physical memory that should be mapped/made
+ *		available, in bytes.
+ * @highmem:	Number of highmem bytes that should be mapped/made available.
+ *
+ * Creates an unlinked temporary file of size (len + highmem) and memory maps
+ * it on the last executable image address (uml_reserved).
+ *
+ * The offset is needed as the length of the total physical memory
+ * (len + highmem) includes the size of the memory used be the executable image,
+ * but the mapped-to address is the last address of the executable image
+ * (uml_reserved == end address of executable image).
+ *
+ * The memory mapped memory of the temporary file is used as backing memory
+ * of all user space processes/kernel tasks.
+ */
 void __init setup_physmem(unsigned long start, unsigned long reserve_end,
 			  unsigned long len, unsigned long long highmem)
 {
 	unsigned long reserve = reserve_end - start;
-	int pfn = PFN_UP(__pa(reserve_end));
-	int delta = (len - reserve) >> PAGE_SHIFT;
-	int err, offset, bootmap_size;
+	unsigned long pfn = PFN_UP(__pa(reserve_end));
+	unsigned long delta = (len - reserve) >> PAGE_SHIFT;
+	unsigned long offset, bootmap_size;
+	long map_size;
+	int err;
+
+	offset = uml_reserved - uml_physmem;
+	map_size = len - offset;
+	if(map_size <= 0) {
+		printf("Too few physical memory! Needed=%d, given=%d\n",
+		       offset, len);
+		exit(1);
+	}
 
 	physmem_fd = create_mem_file(len + highmem);
 
-	offset = uml_reserved - uml_physmem;
 	err = os_map_memory((void *) uml_reserved, physmem_fd, offset,
-			    len - offset, 1, 1, 1);
+			    map_size, 1, 1, 1);
 	if (err < 0) {
 		printf("setup_physmem - mapping %ld bytes of memory at 0x%p "
-		       "failed - errno = %d\n", len - offset,
+		       "failed - errno = %d\n", map_size,
 		       (void *) uml_reserved, err);
 		exit(1);
 	}
@@ -101,8 +109,9 @@
 	 * Special kludge - This page will be mapped in to userspace processes
 	 * from physmem_fd, so it needs to be written out there.
 	 */
-	os_seek_file(physmem_fd, __pa(&__syscall_stub_start));
-	os_write_file(physmem_fd, &__syscall_stub_start, PAGE_SIZE);
+	os_seek_file(physmem_fd, __pa(__syscall_stub_start));
+	os_write_file(physmem_fd, __syscall_stub_start, PAGE_SIZE);
+	os_fsync_file(physmem_fd);
 
 	bootmap_size = init_bootmem(pfn, pfn + delta);
 	free_bootmem(__pa(reserve_end) + bootmap_size,