Re: CHANGE_PV_LIST_LOCK_TO_PHYS is not correct when !NUMA ?

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.


-- 
Andriy Gapon