Introduce XENFEAT_writable_mmu_structures.

Introduce XENFEAT_writable_mmu_structures.

This feature flag indicates to the guest that it is allowable to
use writable LDT, GDT and page table pages.

Signed-off-by: Ian Campbell <Ian.Campbell@XenSource.com>
Index: xen-features/xen/include/public/version.h
===================================================================
--- xen-features.orig/xen/include/public/version.h	2006-01-27 11:27:14.000000000 +0000
+++ xen-features/xen/include/public/version.h	2006-01-27 11:27:14.000000000 +0000
@@ -45,6 +45,9 @@
     uint32_t     submap;        /* OUT: 32-bit submap */
 } xen_feature_info_t;

+#define _XENFEAT_writable_mmu_structures 0
+#define XENFEAT_writable_mmu_structures (1UL<<_XENFEAT_writable_mmu_structures)
+
 #define XENFEAT_NR_SUBMAPS 1

 #endif /* __XEN_PUBLIC_VERSION_H__ */
Index: xen-features/linux-2.6-xen-sparse/arch/xen/i386/mm/pgtable.c
===================================================================
--- xen-features.orig/linux-2.6-xen-sparse/arch/xen/i386/mm/pgtable.c	2006-01-27 11:27:14.000000000 +0000
+++ xen-features/linux-2.6-xen-sparse/arch/xen/i386/mm/pgtable.c	2006-01-27 11:27:14.000000000 +0000
@@ -24,6 +24,7 @@
 #include <asm/io.h>
 #include <asm/mmu_context.h>

+#include <asm-xen/features.h>
 #include <asm-xen/foreign_page.h>
 #include <asm/hypervisor.h>

@@ -391,24 +392,42 @@
 #ifndef CONFIG_XEN_SHADOW_MODE
 void make_lowmem_mmu_page_readonly(void *va)
 {
-	pte_t *pte = virt_to_ptep(va);
-	int rc = HYPERVISOR_update_va_mapping(
+	pte_t *pte;
+	int rc;
+
+	if (xen_feature(writable_mmu_structures))
+		return;
+
+	pte = virt_to_ptep(va);
+	rc = HYPERVISOR_update_va_mapping(
 		(unsigned long)va, pte_wrprotect(*pte), 0);
 	BUG_ON(rc);
 }

 void make_lowmem_mmu_page_writable(void *va)
 {
-	pte_t *pte = virt_to_ptep(va);
-	int rc = HYPERVISOR_update_va_mapping(
+	pte_t *pte;
+	int rc;
+
+	if (xen_feature(writable_mmu_structures))
+		return;
+
+	pte = virt_to_ptep(va);
+	rc = HYPERVISOR_update_va_mapping(
 		(unsigned long)va, pte_mkwrite(*pte), 0);
 	BUG_ON(rc);
 }

 void make_mmu_page_readonly(void *va)
 {
-	pte_t *pte = virt_to_ptep(va);
-	int rc = HYPERVISOR_update_va_mapping(
+	pte_t *pte;
+	int rc;
+
+	if (xen_feature(writable_mmu_structures))
+		return;
+
+	pte = virt_to_ptep(va);
+	rc = HYPERVISOR_update_va_mapping(
 		(unsigned long)va, pte_wrprotect(*pte), 0);
 	if (rc) /* fallback? */
 		xen_l1_entry_update(pte, pte_wrprotect(*pte));
@@ -426,8 +445,14 @@

 void make_mmu_page_writable(void *va)
 {
-	pte_t *pte = virt_to_ptep(va);
-	int rc = HYPERVISOR_update_va_mapping(
+	pte_t *pte;
+	int rc;
+
+	if (xen_feature(writable_mmu_structures))
+		return;
+
+	pte = virt_to_ptep(va);
+	rc = HYPERVISOR_update_va_mapping(
 		(unsigned long)va, pte_mkwrite(*pte), 0);
 	if (rc) /* fallback? */
 		xen_l1_entry_update(pte, pte_mkwrite(*pte));
@@ -443,6 +468,9 @@

 void make_mmu_pages_readonly(void *va, unsigned int nr)
 {
+	if (xen_feature(writable_mmu_structures))
+		return;
+
 	while (nr-- != 0) {
 		make_mmu_page_readonly(va);
 		va = (void *)((unsigned long)va + PAGE_SIZE);
@@ -451,6 +479,8 @@

 void make_mmu_pages_writable(void *va, unsigned int nr)
 {
+	if (xen_feature(writable_mmu_structures))
+		return;
 	while (nr-- != 0) {
 		make_mmu_page_writable(va);
 		va = (void *)((unsigned long)va + PAGE_SIZE);
Index: xen-features/linux-2.6-xen-sparse/arch/xen/x86_64/mm/init.c
===================================================================
--- xen-features.orig/linux-2.6-xen-sparse/arch/xen/x86_64/mm/init.c	2006-01-27 11:27:14.000000000 +0000
+++ xen-features/linux-2.6-xen-sparse/arch/xen/x86_64/mm/init.c	2006-01-27 11:27:18.000000000 +0000
@@ -40,6 +40,8 @@
 #include <asm/proto.h>
 #include <asm/smp.h>

+#include <asm-xen/features.h>
+
 #ifndef Dprintk
 #define Dprintk(x...)
 #endif
@@ -72,6 +74,9 @@
 	pte_t pte, *ptep;
 	unsigned long *page = (unsigned long *) init_level4_pgt;

+	if (xen_feature(writable_mmu_structures))
+		return;
+
 	addr = (unsigned long) page[pgd_index(_va)];
 	addr_to_page(addr, page);

@@ -93,6 +98,9 @@
 	pgd_t *pgd; pud_t *pud; pmd_t *pmd; pte_t pte, *ptep;
 	unsigned long addr = (unsigned long) va;

+	if (xen_feature(writable_mmu_structures))
+		return;
+
 	pgd = pgd_offset_k(addr);
 	pud = pud_offset(pgd, addr);
 	pmd = pmd_offset(pud, addr);
@@ -111,6 +119,9 @@
 	pgd_t *pgd; pud_t *pud; pmd_t *pmd; pte_t pte, *ptep;
 	unsigned long addr = (unsigned long) va;

+	if (xen_feature(writable_mmu_structures))
+		return;
+
 	pgd = pgd_offset_k(addr);
 	pud = pud_offset(pgd, addr);
 	pmd = pmd_offset(pud, addr);
@@ -126,6 +137,9 @@

 void make_mmu_pages_readonly(void *va, unsigned nr)
 {
+	if (xen_feature(writable_mmu_structures))
+		return;
+
 	while (nr-- != 0) {
 		make_mmu_page_readonly(va);
 		va = (void*)((unsigned long)va + PAGE_SIZE);
@@ -134,6 +148,8 @@

 void make_mmu_pages_writable(void *va, unsigned nr)
 {
+	if (xen_feature(writable_mmu_structures))
+		return;
 	while (nr-- != 0) {
 		make_mmu_page_writable(va);
 		va = (void*)((unsigned long)va + PAGE_SIZE);
@@ -385,6 +401,9 @@
 {
 	int readonly = 0;

+	if (xen_feature(writable_mmu_structures))
+		return 0;
+
 	/* Make old and new page tables read-only. */
 	if ((paddr >= (xen_start_info->pt_base - __START_KERNEL_map))
 	    && (paddr < ((table_start << PAGE_SHIFT) + tables_space)))