Re: CHANGE_PV_LIST_LOCK_TO_PHYS is not correct when !NUMA ?

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.