Hi,
Let me guess - kernel is running a privileged code therefore you don't get
it trapped by General Protection #GP exception as you would be when running
in user ring. Anyway have you tried to experiment with other addresses ? I
think you're referring to a logical address here since paging is involved.
Cheers
On Thu, Dec 16, 2010 at 2:38 AM, Luis Useche <use...@gmail.com> wrote:
> Hi Guys,
>
> This is not very related to OpenBSD but perhaps somebody can help me from
> this list.
>
> I need to find what happen when an invalid physical address is accessed
> from
> the kernel for a small project I am doing. My guess is that it will trigger
> some kind of exception trapped by the kernel. I tried this with amd64
> OpenBSD to check what was the behavior. The result is that the invalid
> physical memory is "accessed" with no trap. This does not make much sense.
>
> Here is the code in the kernel:
>
> u = malloc(PAGE_SIZE,0,M_WAITOK);
> *u = 27;
> printf("U 0: %llx %llx
> %d\n",(vaddr_t)u,vtophys((vaddr_t)u),*u);
> pte = vtopte((vaddr_t)u);
> printf("PTE: %llx\n",*pte);
> *pte &= ~PG_FRAME;
> *pte |= 0x0000000230000000UL;
> pmap_update_pg((vaddr_t)u);
> printf("U 1: %llx %llx
> %d\n",(vaddr_t)u,vtophys((vaddr_t)u),*u);
>
> The result in the dmesg is:
>
> USECHE 0: ffff8000001f7000 00000000bf33f000 27
> PTE: bf33f163
> USECHE 1: ffff8000001f7000 0000000230000000 -1
>
> Somebody has a clue on why this does not crash or what happen when the
> invalid physical memory is accessed?
>
> Thanks in advance,
> Luis.
