On 02/17/2017 02:18 PM, Aneesh Kumar K.V wrote:

laurentiu.tudor@nxp.com writes:

quoted

From: Laurentiu Tudor <laurentiu.tudor@nxp.com>

On 32-bit book-e machines, hugepd_ok() does not take
into account null hugepd values, causing this crash at boot:

Unable to handle kernel paging request for data at address 0x80000000
Faulting instruction address: 0xc00182a8
Oops: Kernel access of bad area, sig: 11 [#1]
SMP NR_CPUS=3D24
CoreNet Generic
Modules linked in:
CPU: 1 PID: 1 Comm: swapper/0 Tainted: G        W       4.10.0-rc8-00016=

-g69b1f87 #11

quoted

task: e5050000 task.stack: e5058000
NIP: c00182a8 LR: c001829c CTR: 00007ffe
REGS: e5059c50 TRAP: 0300   Tainted: G        W        (4.10.0-rc8-00016=

-g69b1f87)

quoted

MSR: 00021002 <CE,ME>
   CR: 88428e82  XER: 00000000
DEAR: 80000000 ESR: 00000000
GPR00: c0107510 e5059d00 e5050000 80000000 bffffff1 e5059d0c e5059d08 00=

002017

quoted

GPR08: 00000000 00000000 00000000 00000000 28428e82 00000000 c00027d0 00=

000000

quoted

GPR16: 00000000 00000000 88a28e82 20000000 48422e82 00000000 88a28e84 dd=

004000

quoted

GPR24: e5059e38 00000000 00000000 bffffff1 dd004000 00000001 00029002 bf=

fffff1

quoted

NIP [c00182a8] follow_huge_addr+0x38/0xf0
LR [c001829c] follow_huge_addr+0x2c/0xf0
Call Trace:
[e5059d00] [e5059d00] 0xe5059d00 (unreliable)
[e5059d20] [c0107510] follow_page_mask+0x40/0x3c0
[e5059d80] [c0107958] __get_user_pages+0xc8/0x420
[e5059de0] [c010817c] get_user_pages_remote+0x8c/0x230
[e5059e30] [c013f170] copy_strings+0x110/0x3a0
[e5059ea0] [c013f42c] copy_strings_kernel+0x2c/0x50
[e5059ec0] [c0141324] do_execveat_common+0x474/0x620
[e5059f10] [c01414fc] do_execve+0x2c/0x40
[e5059f20] [c0001f68] try_to_run_init_process+0x18/0x60
[e5059f30] [c000289c] kernel_init+0xcc/0x120
[e5059f40] [c000f1e8] ret_from_kernel_thread+0x5c/0x64
Instruction dump:
bfc10018 7c9f2378 90010024 7fc000a6 7c000146 80630020 38a1000c 38c10008
4bfff869 2c030000 41c20090 81210008 <81430000> 81630004 3860ffea 2f89000=

0

quoted

---[ end trace 4bf94e15fd9fa824 ]---

Which code path is that. That null should be filtered by the if
(pmd_none(pmd)) check in find_linux_pte_or_hugepte right ?

I haven't characterized the issue in detail as i wanted to get the patch=20
out ASAP.
I only noticed that the previous check, that is:

	"signed hpd_val > 0"

vs the new one, that is:

	"unsigned hpd_val & PD_HUGE =3D=3D 0"

evaluate differently for a value of zero: old expression evaluates
to false and the new one to true.

---
Best Regards, Laurentiu=