s390/mm: fix user access page-table walk code

The s390 page-table walk code, used for user copy and futex, currently
cannot handle huge pages. As far as user copy is concerned, that is
not really a problem because those functions will only be used on old
hardware that has no huge page support. But the futex code will also
use pagetable walk functions on current hardware when user space runs
in primary space mode. So, if a futex sits in a huge page, the futex
operation on it will result in a page fault loop or even data
corruption.

This patch adds the code for resolving huge page mappings in the user
access pagetable walk code on s390.
Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/lib/uaccess_pt.c

@@ -2,69 +2,82 @@
  *  User access functions based on page table walks for enhanced
  *  system layout without hardware support.
  *
- *    Copyright IBM Corp. 2006
+ *    Copyright IBM Corp. 2006, 2012
  *    Author(s): Gerald Schaefer (gerald.schaefer@de.ibm.com)
  */
 
 #include <linux/errno.h>
 #include <linux/hardirq.h>
 #include <linux/mm.h>
+#include <linux/hugetlb.h>
 #include <asm/uaccess.h>
 #include <asm/futex.h>
 #include "uaccess.h"
 
-static inline pte_t *follow_table(struct mm_struct *mm, unsigned long addr)
+
+/*
+ * Returns kernel address for user virtual address. If the returned address is
+ * >= -4095 (IS_ERR_VALUE(x) returns true), a fault has occured and the address
+ * contains the (negative) exception code.
+ */
+static __always_inline unsigned long follow_table(struct mm_struct *mm,
+						  unsigned long addr, int write)
 {
 	pgd_t *pgd;
 	pud_t *pud;
 	pmd_t *pmd;
+	pte_t *ptep;
 
 	pgd = pgd_offset(mm, addr);
 	if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
-		return (pte_t *) 0x3a;
+		return -0x3aUL;
 
 	pud = pud_offset(pgd, addr);
 	if (pud_none(*pud) || unlikely(pud_bad(*pud)))
-		return (pte_t *) 0x3b;
+		return -0x3bUL;
 
 	pmd = pmd_offset(pud, addr);
-	if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd)))
-		return (pte_t *) 0x10;
+	if (pmd_none(*pmd))
+		return -0x10UL;
+	if (pmd_huge(*pmd)) {
+		if (write && (pmd_val(*pmd) & _SEGMENT_ENTRY_RO))
+			return -0x04UL;
+		return (pmd_val(*pmd) & HPAGE_MASK) + (addr & ~HPAGE_MASK);
+	}
+	if (unlikely(pmd_bad(*pmd)))
+		return -0x10UL;
+
+	ptep = pte_offset_map(pmd, addr);
+	if (!pte_present(*ptep))
+		return -0x11UL;
+	if (write && !pte_write(*ptep))
+		return -0x04UL;
 
-	return pte_offset_map(pmd, addr);
+	return (pte_val(*ptep) & PAGE_MASK) + (addr & ~PAGE_MASK);
 }
 
 static __always_inline size_t __user_copy_pt(unsigned long uaddr, void *kptr,
 					     size_t n, int write_user)
 {
 	struct mm_struct *mm = current->mm;
-	unsigned long offset, pfn, done, size;
-	pte_t *pte;
+	unsigned long offset, done, size, kaddr;
 	void *from, *to;
 
 	done = 0;
 retry:
 	spin_lock(&mm->page_table_lock);
 	do {
-		pte = follow_table(mm, uaddr);
-		if ((unsigned long) pte < 0x1000)
+		kaddr = follow_table(mm, uaddr, write_user);
+		if (IS_ERR_VALUE(kaddr))
 			goto fault;
-		if (!pte_present(*pte)) {
-			pte = (pte_t *) 0x11;
-			goto fault;
-		} else if (write_user && !pte_write(*pte)) {
-			pte = (pte_t *) 0x04;
-			goto fault;
-		}
 
-		pfn = pte_pfn(*pte);
-		offset = uaddr & (PAGE_SIZE - 1);
+		offset = uaddr & ~PAGE_MASK;
 		size = min(n - done, PAGE_SIZE - offset);
 		if (write_user) {
-			to = (void *)((pfn << PAGE_SHIFT) + offset);
+			to = (void *) kaddr;
 			from = kptr + done;
 		} else {
-			from = (void *)((pfn << PAGE_SHIFT) + offset);
+			from = (void *) kaddr;
 			to = kptr + done;
 		}
 		memcpy(to, from, size);
@@ -75,7 +88,7 @@ static __always_inline size_t __user_copy_pt(unsigned long uaddr, void *kptr,
 	return n - done;
 fault:
 	spin_unlock(&mm->page_table_lock);
-	if (__handle_fault(uaddr, (unsigned long) pte, write_user))
+	if (__handle_fault(uaddr, -kaddr, write_user))
 		return n - done;
 	goto retry;
 }
@@ -84,27 +97,22 @@ static __always_inline size_t __user_copy_pt(unsigned long uaddr, void *kptr,
  * Do DAT for user address by page table walk, return kernel address.
  * This function needs to be called with current->mm->page_table_lock held.
  */
-static __always_inline unsigned long __dat_user_addr(unsigned long uaddr)
+static __always_inline unsigned long __dat_user_addr(unsigned long uaddr,
+						     int write)
 {
 	struct mm_struct *mm = current->mm;
-	unsigned long pfn;
-	pte_t *pte;
+	unsigned long kaddr;
 	int rc;
 
 retry:
-	pte = follow_table(mm, uaddr);
-	if ((unsigned long) pte < 0x1000)
-		goto fault;
-	if (!pte_present(*pte)) {
-		pte = (pte_t *) 0x11;
+	kaddr = follow_table(mm, uaddr, write);
+	if (IS_ERR_VALUE(kaddr))
 		goto fault;
-	}
 
-	pfn = pte_pfn(*pte);
-	return (pfn << PAGE_SHIFT) + (uaddr & (PAGE_SIZE - 1));
+	return kaddr;
 fault:
 	spin_unlock(&mm->page_table_lock);
-	rc = __handle_fault(uaddr, (unsigned long) pte, 0);
+	rc = __handle_fault(uaddr, -kaddr, write);
 	spin_lock(&mm->page_table_lock);
 	if (!rc)
 		goto retry;
@@ -159,11 +167,9 @@ static size_t clear_user_pt(size_t n, void __user *to)
 
 static size_t strnlen_user_pt(size_t count, const char __user *src)
 {
-	char *addr;
 	unsigned long uaddr = (unsigned long) src;
 	struct mm_struct *mm = current->mm;
-	unsigned long offset, pfn, done, len;
-	pte_t *pte;
+	unsigned long offset, done, len, kaddr;
 	size_t len_str;
 
 	if (segment_eq(get_fs(), KERNEL_DS))
@@ -172,19 +178,13 @@ static size_t strnlen_user_pt(size_t count, const char __user *src)
 retry:
 	spin_lock(&mm->page_table_lock);
 	do {
-		pte = follow_table(mm, uaddr);
-		if ((unsigned long) pte < 0x1000)
-			goto fault;
-		if (!pte_present(*pte)) {
-			pte = (pte_t *) 0x11;
+		kaddr = follow_table(mm, uaddr, 0);
+		if (IS_ERR_VALUE(kaddr))
 			goto fault;
-		}
 
-		pfn = pte_pfn(*pte);
-		offset = uaddr & (PAGE_SIZE-1);
-		addr = (char *)(pfn << PAGE_SHIFT) + offset;
+		offset = uaddr & ~PAGE_MASK;
 		len = min(count - done, PAGE_SIZE - offset);
-		len_str = strnlen(addr, len);
+		len_str = strnlen((char *) kaddr, len);
 		done += len_str;
 		uaddr += len_str;
 	} while ((len_str == len) && (done < count));
@@ -192,7 +192,7 @@ static size_t strnlen_user_pt(size_t count, const char __user *src)
 	return done + 1;
 fault:
 	spin_unlock(&mm->page_table_lock);
-	if (__handle_fault(uaddr, (unsigned long) pte, 0))
+	if (__handle_fault(uaddr, -kaddr, 0))
 		return 0;
 	goto retry;
 }
@@ -225,11 +225,10 @@ static size_t copy_in_user_pt(size_t n, void __user *to,
 			      const void __user *from)
 {
 	struct mm_struct *mm = current->mm;
-	unsigned long offset_from, offset_to, offset_max, pfn_from, pfn_to,
-		      uaddr, done, size, error_code;
+	unsigned long offset_max, uaddr, done, size, error_code;
 	unsigned long uaddr_from = (unsigned long) from;
 	unsigned long uaddr_to = (unsigned long) to;
-	pte_t *pte_from, *pte_to;
+	unsigned long kaddr_to, kaddr_from;
 	int write_user;
 
 	if (segment_eq(get_fs(), KERNEL_DS)) {
@@ -242,38 +241,23 @@ static size_t copy_in_user_pt(size_t n, void __user *to,
 	do {
 		write_user = 0;
 		uaddr = uaddr_from;
-		pte_from = follow_table(mm, uaddr_from);
-		error_code = (unsigned long) pte_from;
-		if (error_code < 0x1000)
-			goto fault;
-		if (!pte_present(*pte_from)) {
-			error_code = 0x11;
+		kaddr_from = follow_table(mm, uaddr_from, 0);
+		error_code = kaddr_from;
+		if (IS_ERR_VALUE(error_code))
 			goto fault;
-		}
 
 		write_user = 1;
 		uaddr = uaddr_to;
-		pte_to = follow_table(mm, uaddr_to);
-		error_code = (unsigned long) pte_to;
-		if (error_code < 0x1000)
-			goto fault;
-		if (!pte_present(*pte_to)) {
-			error_code = 0x11;
+		kaddr_to = follow_table(mm, uaddr_to, 1);
+		error_code = (unsigned long) kaddr_to;
+		if (IS_ERR_VALUE(error_code))
 			goto fault;
-		} else if (!pte_write(*pte_to)) {
-			error_code = 0x04;
-			goto fault;
-		}
 
-		pfn_from = pte_pfn(*pte_from);
-		pfn_to = pte_pfn(*pte_to);
-		offset_from = uaddr_from & (PAGE_SIZE-1);
-		offset_to = uaddr_from & (PAGE_SIZE-1);
-		offset_max = max(offset_from, offset_to);
+		offset_max = max(uaddr_from & ~PAGE_MASK,
+				 uaddr_to & ~PAGE_MASK);
 		size = min(n - done, PAGE_SIZE - offset_max);
 
-		memcpy((void *)(pfn_to << PAGE_SHIFT) + offset_to,
-		       (void *)(pfn_from << PAGE_SHIFT) + offset_from, size);
+		memcpy((void *) kaddr_to, (void *) kaddr_from, size);
 		done += size;
 		uaddr_from += size;
 		uaddr_to += size;
@@ -282,7 +266,7 @@ static size_t copy_in_user_pt(size_t n, void __user *to,
 	return n - done;
 fault:
 	spin_unlock(&mm->page_table_lock);
-	if (__handle_fault(uaddr, error_code, write_user))
+	if (__handle_fault(uaddr, -error_code, write_user))
 		return n - done;
 	goto retry;
 }
@@ -341,7 +325,7 @@ int futex_atomic_op_pt(int op, u32 __user *uaddr, int oparg, int *old)
 		return __futex_atomic_op_pt(op, uaddr, oparg, old);
 	spin_lock(&current->mm->page_table_lock);
 	uaddr = (u32 __force __user *)
-		__dat_user_addr((__force unsigned long) uaddr);
+		__dat_user_addr((__force unsigned long) uaddr, 1);
 	if (!uaddr) {
 		spin_unlock(&current->mm->page_table_lock);
 		return -EFAULT;
@@ -378,7 +362,7 @@ int futex_atomic_cmpxchg_pt(u32 *uval, u32 __user *uaddr,
 		return __futex_atomic_cmpxchg_pt(uval, uaddr, oldval, newval);
 	spin_lock(&current->mm->page_table_lock);
 	uaddr = (u32 __force __user *)
-		__dat_user_addr((__force unsigned long) uaddr);
+		__dat_user_addr((__force unsigned long) uaddr, 1);
 	if (!uaddr) {
 		spin_unlock(&current->mm->page_table_lock);
 		return -EFAULT;