Re: CHANGE_PV_LIST_LOCK_TO_PHYS is not correct when !NUMA ?

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.


-- 
Andriy Gapon