uml: speed up page table walking

The previous page table walking code was horribly inefficient.  This patch
replaces it with code taken from elsewhere in the kernel.

Forking from bash is now ~5% faster and page faults are handled ~10% faster.

Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Cc: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/um/kernel/tlb.c

@@ -6,6 +6,7 @@
 #include "linux/mm.h"
 #include "asm/page.h"
 #include "asm/pgalloc.h"
+#include "asm/pgtable.h"
 #include "asm/tlbflush.h"
 #include "choose-mode.h"
 #include "mode_kern.h"
@@ -123,106 +124,143 @@ static int add_mprotect(unsigned long addr, unsigned long len, int r, int w,
 
 #define ADD_ROUND(n, inc) (((n) + (inc)) & ~((inc) - 1))
 
+static inline int update_pte_range(pmd_t *pmd, unsigned long addr,
+				   unsigned long end, struct host_vm_op *ops,
+				   int last_op, int *op_index, int force,
+				   union mm_context *mmu, void **flush,
+				   int (*do_ops)(union mm_context *,
+						 struct host_vm_op *, int, int,
+						 void **))
+{
+	pte_t *pte;
+	int r, w, x, ret = 0;
+
+	pte = pte_offset_kernel(pmd, addr);
+	do {
+		r = pte_read(*pte);
+		w = pte_write(*pte);
+		x = pte_exec(*pte);
+		if (!pte_young(*pte)) {
+			r = 0;
+			w = 0;
+		} else if (!pte_dirty(*pte)) {
+			w = 0;
+		}
+		if(force || pte_newpage(*pte)){
+			if(pte_present(*pte))
+				ret = add_mmap(addr, pte_val(*pte) & PAGE_MASK,
+					       PAGE_SIZE, r, w, x, ops,
+					       op_index, last_op, mmu, flush,
+					       do_ops);
+			else ret = add_munmap(addr, PAGE_SIZE, ops, op_index,
+					      last_op, mmu, flush, do_ops);
+		}
+		else if(pte_newprot(*pte))
+			ret = add_mprotect(addr, PAGE_SIZE, r, w, x, ops,
+					   op_index, last_op, mmu, flush,
+					   do_ops);
+		*pte = pte_mkuptodate(*pte);
+	} while (pte++, addr += PAGE_SIZE, ((addr != end) && !ret));
+	return ret;
+}
+
+static inline int update_pmd_range(pud_t *pud, unsigned long addr,
+				   unsigned long end, struct host_vm_op *ops,
+				   int last_op, int *op_index, int force,
+				   union mm_context *mmu, void **flush,
+				   int (*do_ops)(union mm_context *,
+						 struct host_vm_op *, int, int,
+						 void **))
+{
+	pmd_t *pmd;
+	unsigned long next;
+	int ret = 0;
+
+	pmd = pmd_offset(pud, addr);
+	do {
+		next = pmd_addr_end(addr, end);
+		if(!pmd_present(*pmd)){
+			if(force || pmd_newpage(*pmd)){
+				ret = add_munmap(addr, next - addr, ops,
+						 op_index, last_op, mmu,
+						 flush, do_ops);
+				pmd_mkuptodate(*pmd);
+			}
+		}
+		else ret = update_pte_range(pmd, addr, next, ops, last_op,
+					    op_index, force, mmu, flush,
+					    do_ops);
+	} while (pmd++, addr = next, ((addr != end) && !ret));
+	return ret;
+}
+
+static inline int update_pud_range(pgd_t *pgd, unsigned long addr,
+				   unsigned long end, struct host_vm_op *ops,
+				   int last_op, int *op_index, int force,
+				   union mm_context *mmu, void **flush,
+				   int (*do_ops)(union mm_context *,
+						 struct host_vm_op *, int, int,
+						 void **))
+{
+	pud_t *pud;
+	unsigned long next;
+	int ret = 0;
+
+	pud = pud_offset(pgd, addr);
+	do {
+		next = pud_addr_end(addr, end);
+		if(!pud_present(*pud)){
+			if(force || pud_newpage(*pud)){
+				ret = add_munmap(addr, next - addr, ops,
+						 op_index, last_op, mmu,
+						 flush, do_ops);
+				pud_mkuptodate(*pud);
+			}
+		}
+		else ret = update_pmd_range(pud, addr, next, ops, last_op,
+					    op_index, force, mmu, flush,
+					    do_ops);
+	} while (pud++, addr = next, ((addr != end) && !ret));
+	return ret;
+}
+
 void fix_range_common(struct mm_struct *mm, unsigned long start_addr,
 		      unsigned long end_addr, int force,
 		      int (*do_ops)(union mm_context *, struct host_vm_op *,
 				    int, int, void **))
 {
-	pgd_t *npgd;
-	pud_t *npud;
-	pmd_t *npmd;
-	pte_t *npte;
+	pgd_t *pgd;
 	union mm_context *mmu = &mm->context;
-	unsigned long addr, end;
-	int r, w, x;
 	struct host_vm_op ops[1];
+	unsigned long addr = start_addr, next;
+	int ret = 0, last_op = ARRAY_SIZE(ops) - 1, op_index = -1;
 	void *flush = NULL;
-	int op_index = -1, last_op = ARRAY_SIZE(ops) - 1;
-	int ret = 0;
-
-	if(mm == NULL)
-		return;
+	unsigned long long start_time, end_time;
 
+	start_time = os_nsecs();
 	ops[0].type = NONE;
-	for(addr = start_addr; addr < end_addr && !ret;){
-		npgd = pgd_offset(mm, addr);
-		if(!pgd_present(*npgd)){
-			end = ADD_ROUND(addr, PGDIR_SIZE);
-			if(end > end_addr)
-				end = end_addr;
-			if(force || pgd_newpage(*npgd)){
-				ret = add_munmap(addr, end - addr, ops,
-						 &op_index, last_op, mmu,
-						 &flush, do_ops);
-				pgd_mkuptodate(*npgd);
-			}
-			addr = end;
-			continue;
-		}
-
-		npud = pud_offset(npgd, addr);
-		if(!pud_present(*npud)){
-			end = ADD_ROUND(addr, PUD_SIZE);
-			if(end > end_addr)
-				end = end_addr;
-			if(force || pud_newpage(*npud)){
-				ret = add_munmap(addr, end - addr, ops,
-						 &op_index, last_op, mmu,
-						 &flush, do_ops);
-				pud_mkuptodate(*npud);
-			}
-			addr = end;
-			continue;
-		}
-
-		npmd = pmd_offset(npud, addr);
-		if(!pmd_present(*npmd)){
-			end = ADD_ROUND(addr, PMD_SIZE);
-			if(end > end_addr)
-				end = end_addr;
-			if(force || pmd_newpage(*npmd)){
-				ret = add_munmap(addr, end - addr, ops,
+	pgd = pgd_offset(mm, addr);
+	do {
+		next = pgd_addr_end(addr, end_addr);
+		if(!pgd_present(*pgd)){
+			if (force || pgd_newpage(*pgd)){
+				ret = add_munmap(addr, next - addr, ops,
 						 &op_index, last_op, mmu,
 						 &flush, do_ops);
-				pmd_mkuptodate(*npmd);
+				pgd_mkuptodate(*pgd);
 			}
-			addr = end;
-			continue;
 		}
+		else ret = update_pud_range(pgd, addr, next, ops, last_op,
+					    &op_index, force, mmu, &flush,
+					    do_ops);
+	} while (pgd++, addr = next, ((addr != end_addr) && !ret));
+	end_time = os_nsecs();
+	log_info("total flush time - %Ld nsecs\n", end_time - start_time);
 
-		npte = pte_offset_kernel(npmd, addr);
-		r = pte_read(*npte);
-		w = pte_write(*npte);
-		x = pte_exec(*npte);
-		if (!pte_young(*npte)) {
-			r = 0;
-			w = 0;
-		} else if (!pte_dirty(*npte)) {
-			w = 0;
-		}
-		if(force || pte_newpage(*npte)){
-			if(pte_present(*npte))
-				ret = add_mmap(addr,
-					       pte_val(*npte) & PAGE_MASK,
-					       PAGE_SIZE, r, w, x, ops,
-					       &op_index, last_op, mmu,
-					       &flush, do_ops);
-			else ret = add_munmap(addr, PAGE_SIZE, ops,
-					      &op_index, last_op, mmu,
-					      &flush, do_ops);
-		}
-		else if(pte_newprot(*npte))
-			ret = add_mprotect(addr, PAGE_SIZE, r, w, x, ops,
-					   &op_index, last_op, mmu,
-					   &flush, do_ops);
-
-		*npte = pte_mkuptodate(*npte);
-		addr += PAGE_SIZE;
-	}
 	if(!ret)
 		ret = (*do_ops)(mmu, ops, op_index, 1, &flush);
 
-/* This is not an else because ret is modified above */
+	/* This is not an else because ret is modified above */
 	if(ret) {
 		printk("fix_range_common: failed, killing current process\n");
 		force_sig(SIGKILL, current);