On Fri, Apr 06, 2012 at 12:38:07PM -0400, David Miller wrote:
> From: Sam Ravnborg <sam@xxxxxxxxxxxx>
> Date: Fri, 6 Apr 2012 17:26:19 +0200
>
> > What I think happens is that the MMU is not setup to handle virtual addresses
> > in this area - as this is a much higher address than what we would have seen
> > with the old bootmem allocator. memblock allocates top-down, where bootmem
> > allocates bottom-up.
>
> The first 16MB at KERNBASE is mapped by the head.S code, the rest is
> mapped by arch/sparc/srmmu.c:map_kernel() and similar.
Thanks - it helped me further.
In reality I got page-fault if I tried to access anything at
PAGE_OFFSET + 0xa00000 or above.
So the limit is less than 16 MB.
I found out using a loop like this:
unsigned long paddr;
for (paddr = 0x781000; paddr < 0x1fa0fff; paddr += 0x1000)
{
int tmp;
tmp = *(int *)(PAGE_OFFSET + paddr);
printk(KERN_ERR "paddr=0x%lx (%d)\n", paddr, tmp);
}
And at 0xa00000 is faulted. But at 0x9ff000 it was OK.
So I just introduced a limit of 0xa00000 for __alloc_bootmem_low().
I found no evidence that 0xa00000 will work in general.
So testing is required here :-(
Sam
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