RE: [PATCH] - Align RSE save area

From: Seth, Rohit <rohit.seth_at_intel.com>
Date: 2004-01-17 08:03:37
But the vm_start and vm_end for the vma mapping the rbs space are both
page aligned (irrespective of rbs_bot value).  Right?  Rbs_bot needs to
be just 16 byte aligned and that part is properly done in set_rbs_bot.

rohit

> -----Original Message-----
> From: linux-ia64-owner@vger.kernel.org [mailto:linux-ia64-
> owner@vger.kernel.org] On Behalf Of Jack Steiner
> Sent: Friday, January 16, 2004 12:48 PM
> To: davidm@hpl.hp.com; linux-ia64@vger.kernel.org
> Subject: [PATCH] - Align RSE save area
> 
> 
> Due to a bug in ia64_set_rbs_bot(), the VMA that is created for the
RSE
> save area is not page aligned. The following shows the vma's of a
> process with a bad alignment for the  RSE area (pagesize is 0x4000):
> 
> 	vm_start            vm_end              vm_flags
> 	0x0000000000000000  0x0000000000004000  READ MAYREAD IO
> >>>>	0x600007ffffffe000  0x6000080000002000  READ WRITE MAYREAD
MAYWRITE
> GROWSUP
> 	0x60000ffffff58000  0x60000fffffffc000  READ WRITE MAYREAD
MAYWRITE
> MAYEXEC GROWSDOWN
> 
> This is not expected nor correctly handled by the VM code.
> 
> 
> When a process that has an unaligned VMA exits, the teardown of the
> process
> address space fails. The result is that a pte may be left in a
pagetable
> page
> when the pagetable page is freed. Pagetable pages are assumed to be
all
> zeros
> and are cached in a quicklist for subsequent reuse. Pagetable pages
> that are allocated from this quicklist not zeroed out on reuse (they
are
> *suppose*
> to be zero).
> 
> The process that reuses the pagetable page will "inherit" the stale
pages
> left
> over from the previous process that used the pagetable page. This was
> causing
> really weird failures.
> 
> 
> 
> Here is a proposed fix:
> 
> 
> --- linux.base/arch/ia64/mm/init.c	Fri Jan  9 00:59:26 2004
> +++ linux/arch/ia64/mm/init.c	Fri Jan 16 14:40:14 2004
> @@ -98,7 +98,7 @@
> 
>  	if (stack_size > MAX_USER_STACK_SIZE)
>  		stack_size = MAX_USER_STACK_SIZE;
> -	current->thread.rbs_bot = STACK_TOP - stack_size;
> +	current->thread.rbs_bot = PAGE_ALIGN(STACK_TOP - stack_size);
>  }
> 
>  /*
> 
> 
> 
> --
> Thanks
> 
> Jack Steiner (steiner@sgi.com)          651-683-5302
> Principal Engineer                      SGI - Silicon Graphics, Inc.
> 
> 
> -
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Received on Fri Jan 16 16:05:19 2004

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