[Lguest] Error inserting lg: Cannot allocate memory

[Fabio Checconi]

> From: Rusty Russell <rusty at rustcorp.com.au>
> Date: Tue, Mar 04, 2008 09:11:25PM +1100
>
...
> lguest should pass a valid "end" parameter, not some random constant.
> 
> Signed-off-by: Rusty Russell <rusty at rustcorp.com.au>
> Cc: Robert Bragg <robert at sixbynine.org>
> 
> diff -r f5dc1442dc61 drivers/lguest/core.c
> --- a/drivers/lguest/core.c	Tue Mar 04 14:21:38 2008 +1100
> +++ b/drivers/lguest/core.c	Tue Mar 04 21:06:41 2008 +1100
> @@ -71,9 +71,11 @@ static __init int map_switcher(void)
>  
>  	/* Now we reserve the "virtual memory area" we want: 0xFFC00000
>  	 * (SWITCHER_ADDR).  We might not get it in theory, but in practice
> -	 * it's worked so far. */
> +	 * it's worked so far.  The +1 is because __get_vm_area allocates a
> +	 * guard page, so we need space for that. */
>  	switcher_vma = __get_vm_area(TOTAL_SWITCHER_PAGES * PAGE_SIZE,
> -				       VM_ALLOC, SWITCHER_ADDR, VMALLOC_END);
> +				     VM_ALLOC, SWITCHER_ADDR, SWITCHER_ADDR
> +				     + (TOTAL_SWITCHER_PAGES+1) * PAGE_SIZE);
>  	if (!switcher_vma) {
>  		err = -ENOMEM;
>  		printk("lguest: could not map switcher pages high\n");

With the original .config, VMALLOC_END was lower than SWITCHER_ADDR,
with this patch we may be forcing an allocation beyond VMALLOC_END,
and this may cause the allocated region to fall in the fixmap/PKMAP
area.

VMALLOC_END does not seem to be a random constant, as, e.g.,
get_vm_area() is still returning:

	__get_vm_area(size, flags, VMALLOC_START, VMALLOC_END)

I apologize in advance if I'm missing something trivial here.