[PATCH] powerpc: Make hugepage mappings respect hint addresses

Currently, the powerpc version of hugetlb_get_unmapped_area() entirely
ignores the hint address.  The only way to get a hugepage mapping at a
specified address is with MAP_FIXED, in which case there's no way
(short of parsing /proc/self/maps) for userspace to tell if it will
clobber an existing mapping.  This is inconvenient, so the patch below
makes hugepage mappings use the given hint address if possible.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>

diff --git a/arch/powerpc/mm/hugetlbpage.c b/arch/powerpc/mm/hugetlbpage.c
index 54131b8..f6fe3ea 100644 (file)
--- a/arch/powerpc/mm/hugetlbpage.c
+++ b/arch/powerpc/mm/hugetlbpage.c
@@ -549,6 +549,17 @@ fail:
        return addr;
 }
 
+static int htlb_check_hinted_area(unsigned long addr, unsigned long len)
+{
+       struct vm_area_struct *vma;
+
+       vma = find_vma(current->mm, addr);
+       if (!vma || ((addr + len) <= vma->vm_start))
+               return 0;
+
+       return -ENOMEM;
+}
+
 static unsigned long htlb_get_low_area(unsigned long len, u16 segmask)
 {
        unsigned long addr = 0;
@@ -609,6 +620,7 @@ unsigned long hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
 {
        int lastshift;
        u16 areamask, curareas;
+       struct vm_area_struct *vma;
 
        if (HPAGE_SHIFT == 0)
                return -EINVAL;
@@ -618,15 +630,28 @@ unsigned long hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
        if (!cpu_has_feature(CPU_FTR_16M_PAGE))
                return -EINVAL;
 
+       /* Paranoia, caller should have dealt with this */
+       BUG_ON((addr + len)  < addr);
+
        if (test_thread_flag(TIF_32BIT)) {
+               /* Paranoia, caller should have dealt with this */
+               BUG_ON((addr + len) > 0x100000000UL);
+
                curareas = current->mm->context.low_htlb_areas;
 
-               /* First see if we can do the mapping in the existing
-                * low areas */
+               /* First see if we can use the hint address */
+               if (addr && (htlb_check_hinted_area(addr, len) == 0)) {
+                       areamask = LOW_ESID_MASK(addr, len);
+                       if (open_low_hpage_areas(current->mm, areamask) == 0)
+                               return addr;
+               }
+
+               /* Next see if we can map in the existing low areas */
                addr = htlb_get_low_area(len, curareas);
                if (addr != -ENOMEM)
                        return addr;
 
+               /* Finally go looking for areas to open */
                lastshift = 0;
                for (areamask = LOW_ESID_MASK(0x100000000UL-len, len);
                     ! lastshift; areamask >>=1) {
@@ -641,12 +666,22 @@ unsigned long hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
        } else {
                curareas = current->mm->context.high_htlb_areas;
 
-               /* First see if we can do the mapping in the existing
-                * high areas */
+               /* First see if we can use the hint address */
+               /* We discourage 64-bit processes from doing hugepage
+                * mappings below 4GB (must use MAP_FIXED) */
+               if ((addr >= 0x100000000UL)
+                   && (htlb_check_hinted_area(addr, len) == 0)) {
+                       areamask = HTLB_AREA_MASK(addr, len);
+                       if (open_high_hpage_areas(current->mm, areamask) == 0)
+                               return addr;
+               }
+
+               /* Next see if we can map in the existing high areas */
                addr = htlb_get_high_area(len, curareas);
                if (addr != -ENOMEM)
                        return addr;
 
+               /* Finally go looking for areas to open */
                lastshift = 0;
                for (areamask = HTLB_AREA_MASK(TASK_SIZE_USER64-len, len);
                     ! lastshift; areamask >>=1) {