Re: Fatal trap 12: page fault on Acer Chromebook 720 (peppy)

>> On 24. Aug 2018, at 22:39, Konstantin Belousov <kostikbel_at_gmail.com> wrote:
>> 
>> On Fri, Aug 24, 2018 at 10:32:06PM +0200, Michael Gmelin wrote:
>> 
>> 
>>> On 24. Aug 2018, at 21:59, Konstantin Belousov <kostikbel_at_gmail.com> wrote:
>>> Please apply the following debugging patch on top of the previous 'fix'.
>>> You need debug.late_console=0.
>> 
>> Unfortunately debug.late_console=0 doesn???t work on this machine (no more output on the console), I tried that earlier in this thread - hence the slightly complicated debugging code I had to add to see the contents of physmap.
>> 
>> I could run this code after boot (feeding it an identical physmap) to get debug output, would this make sense?
> Yes, with exactly the same physmap[].
> 
> Really, I do not need exactly the output from my patch, but just make it
> clear why is_kernel_paddr() did not triggered selection from different
> location.

I have to apologize, something went wrong
when I applied your previous fix, so it was never really used when I tested.

Now, with the patch applied correctly, the machine actually boots.

Before calling init_ops.mp_bootaddress in
getmemsize (machdep.c), physmap looks like this:

physmap_idx: 8
i mem atop
0 0x0 0x0
1 0x30000 0x30
2 0x40000 0x40
3 0x9e400 0x9e
4 0x100000 0x100
5 0xf00000 0xf00
6 0x1000000 0x1000
7 0x7bf7a000 0x7bf7a
8 0x100000000 0x100000
9 0x100600000 0x100600
10 0x0 0x0

With your patch, it looks like this now
(after calling getmemsize)

0 0x0 0x0
1 0x30000 0x30
2 0x40000 0x40
3 0x9e400 0x9e
4 0x100000 0x100
5 0xf00000 0xf00
6 0x1000000 0x1000
7 0x7bf77000 0x7bf77
8 0x100000000 0x100000
9 0x100600000 0x100600
10 0x0 0x0
PAGETABLES is 0x7bf77000

So I guess this means that the gap is now at the last three pages of [0x1000, 0x7bf7a[.

If this is what was intended, I guess it's good, as the machine boots okay now.

Sorry again for the extra roundtrip, the patched file was simply in the wrong path.

Yours,
Michael

p.s. Please see below the patched version of
mp_machdep.c I used for testing (should match yours):

...
#define    AP_BOOTPT_SZ        (PAGE_SIZE * 3)

extern    struct pcpu __pcpu[];

/* Temporary variables for init_secondary()  */
char *doublefault_stack;
char *mce_stack;
char *nmi_stack;
char *dbg_stack;

/*
* Local data and functions.
*/

static int    start_ap(int apic_id);

static bool
is_kernel_paddr(vm_paddr_t pa)
{

 return (pa >= trunc_2mpage(btext - KERNBASE) &&
    pa < round_page(_end - KERNBASE));
}

static bool
is_mpboot_good(vm_paddr_t start, vm_paddr_t end)
{

 return (start + AP_BOOTPT_SZ <= GiB(4) &&
     end >= start + AP_BOOTPT_SZ && atop(end) < Maxmem);
}

/*
* Calculate usable address in base memory for AP trampoline code.
*/
void
mp_bootaddress(vm_paddr_t *physmap, unsigned int *physmap_idx)
{
 vm_paddr_t start, end;
 unsigned int i;
 bool allocated;

 alloc_ap_trampoline(physmap, physmap_idx);

 /*
  * Find a memory region big enough below the 4GB boundary to
  * store the initial page tables.  Region must be mapped by
  * the direct map.
  *
  * Note that it needs to be aligned to a page boundary.
  */
 allocated = false;
 for (i = *physmap_idx; i <= *physmap_idx; i -= 2) {
     /*
      * First, try to chomp at the start of the physmap region.
      * Kernel binary might claim it already.
      */
     start = round_page(physmap[i]);
     end = trunc_page(physmap[i + 1]);
     if (is_mpboot_good(start, end) &&
         !is_kernel_paddr(start) && !is_kernel_paddr(end - 1)) {
         allocated = true;
         physmap[i] = start + AP_BOOTPT_SZ;
         break;
     }

     /*
      * Second, try to chomp at the end.  Again, check
      * against kernel.
      */
     end = trunc_page(physmap[i + 1]);
     start = end - AP_BOOTPT_SZ;
     if (start >= physmap[i] && is_mpboot_good(start, end) &&
         !is_kernel_paddr(start) && !is_kernel_paddr(end - 1)) {
         allocated = true;
         physmap[i + 1] = start;
         break;
     }
 }
 if (allocated) {
     mptramp_pagetables = start;
     if (physmap[i] == physmap[i + 1] && *physmap_idx != 0) {
         memmove(&physmap[i], &physmap[i + 2],
             sizeof(*physmap) * (*physmap_idx - i + 2));
         *physmap_idx -= 2;
     }
 } else {
     mptramp_pagetables = trunc_page(boot_address) - AP_BOOTPT_SZ;
     if (bootverbose)
         printf(
"Cannot find enough space for the initial AP page tables, placing them at %#x",
             mptramp_pagetables);
 }
}
...