lguest: assume Switcher text is a single page.

ie. SHARED_SWITCHER_PAGES == 1.  It is well under a page, and it's a
minor simplification: it's nice to have *one* simplification in a
patch series!
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

arch/x86/include/asm/lguest.h

@@ -11,11 +11,8 @@
 
 #define GUEST_PL 1
 
-/* Every guest maps the core switcher code. */
-#define SHARED_SWITCHER_PAGES \
-	DIV_ROUND_UP(end_switcher_text - start_switcher_text, PAGE_SIZE)
-/* Pages for switcher itself, then two pages per cpu */
-#define TOTAL_SWITCHER_PAGES (SHARED_SWITCHER_PAGES + 2 * nr_cpu_ids)
+/* Page for Switcher text itself, then two pages per cpu */
+#define TOTAL_SWITCHER_PAGES (1 + 2 * nr_cpu_ids)
 
 /* We map at -4M (-2M for PAE) for ease of mapping (one PTE page). */
 #ifdef CONFIG_X86_PAE

drivers/lguest/core.c

@@ -52,6 +52,13 @@ static __init int map_switcher(void)
 	 * easy.
 	 */
 
+	/* We assume Switcher text fits into a single page. */
+	if (end_switcher_text - start_switcher_text > PAGE_SIZE) {
+		printk(KERN_ERR "lguest: switcher text too large (%zu)\n",
+		       end_switcher_text - start_switcher_text);
+		return -EINVAL;
+	}
+
 	/*
 	 * We allocate an array of struct page pointers.  map_vm_area() wants
 	 * this, rather than just an array of pages.
@@ -326,7 +333,7 @@ static int __init init(void)
 		goto out;
 
 	/* Now we set up the pagetable implementation for the Guests. */
-	err = init_pagetables(switcher_pages, SHARED_SWITCHER_PAGES);
+	err = init_pagetables(switcher_pages);
 	if (err)
 		goto unmap;
 

drivers/lguest/lg.h

@@ -15,7 +15,7 @@
 #include <asm/lguest.h>
 
 void free_pagetables(void);
-int init_pagetables(struct page **switcher_pages, unsigned int pages);
+int init_pagetables(struct page **switcher_pages);
 
 struct pgdir {
 	unsigned long gpgdir;

drivers/lguest/page_tables.c

@@ -1079,25 +1079,20 @@ static void free_switcher_pte_pages(void)
 
 /*H:520
  * Setting up the Switcher PTE page for given CPU is fairly easy, given
- * the CPU number and the "struct page"s for the Switcher code itself.
- *
- * Currently the Switcher is less than a page long, so "pages" is always 1.
+ * the CPU number and the "struct page"s for the Switcher and per-cpu pages.
  */
 static __init void populate_switcher_pte_page(unsigned int cpu,
-					      struct page *switcher_pages[],
-					      unsigned int pages)
+					      struct page *switcher_pages[])
 {
-	unsigned int i;
 	pte_t *pte = switcher_pte_page(cpu);
+	int i;
 
-	/* The first entries are easy: they map the Switcher code. */
-	for (i = 0; i < pages; i++) {
-		set_pte(&pte[i], mk_pte(switcher_pages[i],
+	/* The first entries maps the Switcher code. */
+	set_pte(&pte[0], mk_pte(switcher_pages[0],
 				__pgprot(_PAGE_PRESENT|_PAGE_ACCESSED)));
-	}
 
 	/* The only other thing we map is this CPU's pair of pages. */
-	i = pages + cpu*2;
+	i = 1 + cpu*2;
 
 	/* First page (Guest registers) is writable from the Guest */
 	set_pte(&pte[i], pfn_pte(page_to_pfn(switcher_pages[i]),
@@ -1128,7 +1123,7 @@ static __init void populate_switcher_pte_page(unsigned int cpu,
  * At boot or module load time, init_pagetables() allocates and populates
  * the Switcher PTE page for each CPU.
  */
-__init int init_pagetables(struct page **switcher_pages, unsigned int pages)
+__init int init_pagetables(struct page **switcher_pages)
 {
 	unsigned int i;
 
@@ -1138,7 +1133,7 @@ __init int init_pagetables(struct page **switcher_pages, unsigned int pages)
 			free_switcher_pte_pages();
 			return -ENOMEM;
 		}
-		populate_switcher_pte_page(i, switcher_pages, pages);
+		populate_switcher_pte_page(i, switcher_pages);
 	}
 	return 0;
 }

drivers/lguest/x86/core.c

@@ -62,11 +62,10 @@ static unsigned long switcher_offset(void)
 	return switcher_addr - (unsigned long)start_switcher_text;
 }
 
-/* This cpu's struct lguest_pages. */
+/* This cpu's struct lguest_pages (after the Switcher text page) */
 static struct lguest_pages *lguest_pages(unsigned int cpu)
 {
-	return &(((struct lguest_pages *)
-		  (switcher_addr + SHARED_SWITCHER_PAGES*PAGE_SIZE))[cpu]);
+	return &(((struct lguest_pages *)(switcher_addr + PAGE_SIZE))[cpu]);
 }
 
 static DEFINE_PER_CPU(struct lg_cpu *, lg_last_cpu);