Re: CHANGE_PV_LIST_LOCK_TO_PHYS is not correct when !NUMA ?

On 09/05/2020 19:50, Konstantin Belousov wrote:
> On Sat, May 09, 2020 at 07:16:27PM +0300, Andriy Gapon wrote:
>> On 09/05/2020 19:13, Konstantin Belousov wrote:
>>> On Sat, May 09, 2020 at 06:52:24PM +0300, Andriy Gapon wrote:
>>>> On 08/05/2020 19:15, Konstantin Belousov wrote:
>>>>> On Fri, May 08, 2020 at 06:53:24PM +0300, Andriy Gapon wrote:
>>>>>>
>>>>>> I have a reproducible panic with a custom kernel without option NUMA while using
>>>>>> amdgpu driver from linuxkpi-based drm:
>>>>>>
>>>>>> panic: address 41ec00000 beyond the last segment
>>>>>>
>>>>>> I did some quick debugging and the panic happens when Xorg server tries to
>>>>>> access a frame buffer (or something like that).  There is a page fault that gets
>>>>>> satisfied by ttm with a fictitious page.
>>>>>>
>>>>>> The stack trace is:
>>>>>> #11 0xffffffff808031a3 in panic (fmt=0xffffffff8119a998 <cnputs_mtx>
>>>>>> "5\003ʀ\377\377\377\377") at /usr/devel/git/motil/sys/kern/kern_shutdown.c:839
>>>>>> #12 0xffffffff80bbc552 in pmap_enter (pmap=<optimized out>, va=34504441856,
>>>>>> m=<optimized out>, prot=<optimized out>, flags=<optimized out>, psind=<optimized
>>>>>> out>) at /usr/devel/git/motil/sys/amd64/amd64/pmap.c:6035
>>>>>> #13 0xffffffff80b288be in vm_fault_populate (fs=<optimized out>) at
>>>>>> /usr/devel/git/motil/sys/vm/vm_fault.c:519
>>>>>> #14 vm_fault_allocate (fs=<optimized out>) at
>>>>>> /usr/devel/git/motil/sys/vm/vm_fault.c:1032
>>>>>> #15 vm_fault (map=<optimized out>, vaddr=<optimized out>, fault_type=<optimized
>>>>>> out>, fault_flags=<optimized out>, m_hold=<optimized out>) at
>>>>>> /usr/devel/git/motil/sys/vm/vm_fault.c:1342
>>>>>> #16 0xffffffff80b26e7e in vm_fault_trap (map=0xfffffe0017cd39e8,
>>>>>> vaddr=<optimized out>, fault_type=<optimized out>, fault_flags=0,
>>>>>> signo=0xfffffe00a810dbc4, ucode=0xfffffe00a810dbc0) at
>>>>>> /usr/devel/git/motil/sys/vm/vm_fault.c:589
>>>>>> #17 0xffffffff80bcf89c in trap_pfault (frame=0xfffffe00a810dc00,
>>>>>> usermode=<optimized out>, signo=<optimized out>, ucode=0xffffffff80853250
>>>>>> <putchar>) at /usr/devel/git/motil/sys/amd64/amd64/trap.c:821
>>>>>> #18 0xffffffff80bceeec in trap (frame=0xfffffe00a810dc00) at
>>>>>> /usr/devel/git/motil/sys/amd64/amd64/trap.c:34
>>>>>>
>>>>>>
>>>>>> The line number in pmap_enter() is incorrect, I guess because of optimizations.
>>>>>> The assert seems to be reached via pmap_enter -> CHANGE_PV_LIST_LOCK_TO_PHYS ->
>>>>>> PHYS_TO_PV_LIST_LOCK -> pa_index().
>>>>>>
>>>>>> The panic in correct in that the page is fictitious and its physical address is
>>>>>> beyond the end of real physical memory.
>>>>>> It seems that NUMA PHYS_TO_PV_LIST_LOCK() is aware of such pages, but !NUMA one
>>>>>> is not.
>>>>>
>>>>> I think you can remove this assert.  pa_index() is always taken by
>>>>> % NVP_LIST_LOCKS, because fictitious mappings are not promoted.
>>>>>
>>>>> Try that and commit if it works for you.
>>>>
>>>> I tried this change:
>>>> diff --git a/sys/amd64/amd64/pmap.c b/sys/amd64/amd64/pmap.c
>>>> index 4deed86a76d1a..b834b7f0388b7 100644
>>>> --- a/sys/amd64/amd64/pmap.c
>>>> +++ b/sys/amd64/amd64/pmap.c
>>>> _at__at_ -345,7 +345,7 _at__at_ pmap_pku_mask_bit(pmap_t pmap)
>>>>  #define	NPV_LIST_LOCKS	MAXCPU
>>>>
>>>>  #define	PHYS_TO_PV_LIST_LOCK(pa)	\
>>>> -			(&pv_list_locks[pa_index(pa) % NPV_LIST_LOCKS])
>>>> +			(&pv_list_locks[((pa) >> PDRSHIFT) % NPV_LIST_LOCKS])
>>>>  #endif
>>>>
>>>>  #define	CHANGE_PV_LIST_LOCK_TO_PHYS(lockp, pa)	do {	\
>>>>
>>>> It fixed the original problem, but I got a new panic.
>>>> "DI already started" in pmap_remove() -> pmap_delayed_invl_start_u().
>>>> I guess that !NUMA variant does not get much testing, so I'll probably just
>>>> stick with the default.
>>> Why didn't you just removed the KASSERT from pa_index ?
>>
>> Well, I thought it might be useful in the NUMA case.
>> pa_index() definition is shared between both cases.
> Might be define the macro two times, for NUMA/non-NUMA.  non-NUMA case
> does not need the assert, because users take it mod NPV_LIST_LOCKS.
> 

I still don't see how that could help with "DI already started" panic.

-- 
Andriy Gapon