Re: [PATCH] linux/x86-64: allow kernel init memory to be freed

["Jan Beulich" <jbeulich@novell.com>]

>> So - would you be okay with taking the full-blown patch (probably not, as it
>> touches another file not currently in the sparse tree), or should I create a
>> __make_page_inaccessible() function along the lines of
>> __make_page_readonly()/__make_page_writable()?
>
>Yeah, I'll go with __make_page_inaccessible(). :-)

I decided against an extra function, after realizing that the vmalloc area
handling part is useless for this case, and thus the code is more reasonable
to be put in explicitly. And also because I hope to get this code out again
via a mainline change. Here's the updated patch.

Subject: allow kernel init memory to be freed

Signed-off-by: Jan Beulich <jbeulich@novell.com>

Index: head-2007-02-08/arch/x86_64/mm/init-xen.c
===================================================================
--- head-2007-02-08.orig/arch/x86_64/mm/init-xen.c	2007-02-27 15:00:16.000000000 +0100
+++ head-2007-02-08/arch/x86_64/mm/init-xen.c	2007-02-27 15:00:42.000000000 +0100
@@ -102,14 +102,11 @@ static void __meminit early_make_page_re
 		BUG();
 }
 
-void make_page_readonly(void *va, unsigned int feature)
+static void __make_page_readonly(void *va)
 {
 	pgd_t *pgd; pud_t *pud; pmd_t *pmd; pte_t pte, *ptep;
 	unsigned long addr = (unsigned long) va;
 
-	if (xen_feature(feature))
-		return;
-
 	pgd = pgd_offset_k(addr);
 	pud = pud_offset(pgd, addr);
 	pmd = pmd_offset(pud, addr);
@@ -120,17 +117,14 @@ void make_page_readonly(void *va, unsign
 		xen_l1_entry_update(ptep, pte); /* fallback */
 
 	if ((addr >= VMALLOC_START) && (addr < VMALLOC_END))
-		make_page_readonly(__va(pte_pfn(pte) << PAGE_SHIFT), feature);
+		__make_page_readonly(__va(pte_pfn(pte) << PAGE_SHIFT));
 }
 
-void make_page_writable(void *va, unsigned int feature)
+static void __make_page_writable(void *va)
 {
 	pgd_t *pgd; pud_t *pud; pmd_t *pmd; pte_t pte, *ptep;
 	unsigned long addr = (unsigned long) va;
 
-	if (xen_feature(feature))
-		return;
-
 	pgd = pgd_offset_k(addr);
 	pud = pud_offset(pgd, addr);
 	pmd = pmd_offset(pud, addr);
@@ -141,7 +135,19 @@ void make_page_writable(void *va, unsign
 		xen_l1_entry_update(ptep, pte); /* fallback */
 
 	if ((addr >= VMALLOC_START) && (addr < VMALLOC_END))
-		make_page_writable(__va(pte_pfn(pte) << PAGE_SHIFT), feature);
+		__make_page_writable(__va(pte_pfn(pte) << PAGE_SHIFT));
+}
+
+void make_page_readonly(void *va, unsigned int feature)
+{
+	if (!xen_feature(feature))
+		__make_page_readonly(va);
+}
+
+void make_page_writable(void *va, unsigned int feature)
+{
+	if (!xen_feature(feature))
+		__make_page_writable(va);
 }
 
 void make_pages_readonly(void *va, unsigned nr, unsigned int feature)
@@ -150,7 +156,7 @@ void make_pages_readonly(void *va, unsig
 		return;
 
 	while (nr-- != 0) {
-		make_page_readonly(va, feature);
+		__make_page_readonly(va);
 		va = (void*)((unsigned long)va + PAGE_SIZE);
 	}
 }
@@ -161,7 +167,7 @@ void make_pages_writable(void *va, unsig
 		return;
 
 	while (nr-- != 0) {
-		make_page_writable(va, feature);
+		__make_page_writable(va);
 		va = (void*)((unsigned long)va + PAGE_SIZE);
 	}
 }
@@ -1028,11 +1034,6 @@ void free_init_pages(char *what, unsigne
 
 void free_init_pages(char *what, unsigned long begin, unsigned long end)
 {
-#ifdef __DO_LATER__
-	/*
-	 * Some pages can be pinned, but some are not. Unpinning such pages 
-	 * triggers BUG(). 
-	 */
 	unsigned long addr;
 
 	if (begin >= end)
@@ -1044,25 +1045,27 @@ void free_init_pages(char *what, unsigne
 		init_page_count(virt_to_page(addr));
 		memset((void *)(addr & ~(PAGE_SIZE-1)),
 		       POISON_FREE_INITMEM, PAGE_SIZE); 
-		make_page_writable(
-			__va(__pa(addr)), XENFEAT_writable_page_tables);
-		/*
-		 * Make pages from __PAGE_OFFSET address as well
-		 */
-		make_page_writable(
-			(void *)addr, XENFEAT_writable_page_tables);
+		if (addr >= __START_KERNEL_map) {
+			/* make_readonly() reports all kernel addresses. */
+			__make_page_writable(__va(__pa(addr)));
+			if (HYPERVISOR_update_va_mapping(addr, __pte(0), 0)) {
+				pgd_t *pgd = pgd_offset_k(addr);
+				pud_t *pud = pud_offset(pgd, addr);
+				pmd_t *pmd = pmd_offset(pud, addr);
+				pte_t *pte = pte_offset_kernel(pmd, addr);
+
+				xen_l1_entry_update(pte, __pte(0)); /* fallback */
+			}
+		}
 		free_page(addr);
 		totalram_pages++;
 	}
-#endif
 }
 
 void free_initmem(void)
 {
-#ifdef __DO_LATER__
 	memset(__initdata_begin, POISON_FREE_INITDATA,
 		__initdata_end - __initdata_begin);
-#endif
 	free_init_pages("unused kernel memory",
 			(unsigned long)(&__init_begin),
 			(unsigned long)(&__init_end));