[lkml]   [2002]   [Jul]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
Patch in this message
Subjectpage table page->index
I found a situation where page->index for a pagetable page can be set
to 0 instead of the correct value. This means that ptep_to_address
will return the wrong answer. The problem occurs when remap_pmd_range
calls pte_alloc_map and pte_alloc_map needs to allocate a new pte
page, because remap_pmd_range has masked off the top bits of the
address (to avoid overflow in the computation of `end'), and it passes
the masked address to pte_alloc_map.

Now we presumably don't need to get from the physical pages mapped by
remap_page_range back to the ptes mapping them. But we could easily
map some normal pages using ptes in that pagetable page subsequently,
and when we call ptep_to_address on their ptes it will give the wrong

The patch below fixes the problem.

There is a more general question this brings up - some of the
procedures which iterate over ranges of ptes will do the wrong thing
if the end of the address range is too close to ~0UL, while others are
OK. Is this a problem in practice? On i386, ppc, and the 64-bit
architectures it isn't since user addresses can't go anywhere near
~0UL, but what about arm or m68k for instance?

And BTW, being able to go from a pte pointer to the mm and virtual
address that that pte maps is an extremely useful thing on ppc, since
it will enable me to do MMU hash-table management at set_pte (and
ptep_*) time and thus avoid the extra traversal of the pagetables that
I am currently doing in flush_tlb_*. So if you do decide to back out
rmap, please leave in the hooks for setting page->mapping and
page->index on pagetable pages.


diff -urN linux-2.5/mm/memory.c pmac-2.5/mm/memory.c
--- linux-2.5/mm/memory.c Thu Jul 18 05:27:58 2002
+++ pmac-2.5/mm/memory.c Sat Jul 27 15:42:18 2002
@@ -863,18 +863,19 @@
static inline int remap_pmd_range(struct mm_struct *mm, pmd_t * pmd, unsigned long address, unsigned long size,
unsigned long phys_addr, pgprot_t prot)
- unsigned long end;
+ unsigned long base, end;

+ base = address & PGDIR_MASK;
address &= ~PGDIR_MASK;
end = address + size;
if (end > PGDIR_SIZE)
phys_addr -= address;
do {
- pte_t * pte = pte_alloc_map(mm, pmd, address);
+ pte_t * pte = pte_alloc_map(mm, pmd, base + address);
if (!pte)
return -ENOMEM;
- remap_pte_range(pte, address, end - address, address + phys_addr, prot);
+ remap_pte_range(pte, base + address, end - address, address + phys_addr, prot);
address = (address + PMD_SIZE) & PMD_MASK;
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

 \ /
  Last update: 2005-03-22 13:22    [W:0.039 / U:2.604 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site