The arm64 fork-then-swap-out-then-swap-in failures: a program source for exploring them

[Mark Millard]

On 2017-Apr-9, at 5:10 PM, Mark Millard <markmi at dsl-only.net> wrote:

> On 2017-Apr-9, at 10:24 AM, Mark Millard <markmi at dsl-only.net> wrote:
> 
>> On 2017-Apr-9, at 5:27 AM, Konstantin Belousov <kostikbel at gmail.com> wrote:
> 
>> 
>>> Hmm, could you try the following patch, I did not even compiled it.
>> 
>> I'll try it later today.
>> 
>>> diff --git a/sys/arm64/arm64/pmap.c b/sys/arm64/arm64/pmap.c
>>> index 3d5756ba891..55aa402eb1c 100644
>>> --- a/sys/arm64/arm64/pmap.c
>>> +++ b/sys/arm64/arm64/pmap.c
>>> @@ -2481,6 +2481,11 @@ pmap_protect(pmap_t pmap, vm_offset_t sva, vm_offset_t eva, vm_prot_t prot)
>>> 		    sva += L3_SIZE) {
>>> 			l3 = pmap_load(l3p);
>>> 			if (pmap_l3_valid(l3)) {
>>> +				if ((l3 & ATTR_SW_MANAGED) &&
>>> +				    pmap_page_dirty(l3)) {
>>> +					vm_page_dirty(PHYS_TO_VM_PAGE(l3 &
>>> +					    ~ATTR_MASK));
>>> +				}
>>> 				pmap_set(l3p, ATTR_AP(ATTR_AP_RO));
>>> 				PTE_SYNC(l3p);
>>> 				/* XXX: Use pmap_invalidate_range */
> 
> 
> Preliminary testing indicates that this fixes the
> some-pages-become-zero problem for fork-then-swapout/in.
> 
> Thanks!
> 
> I'll see if a buildworld can go through without being stopped
> by the type of issue. But that will take a while. (It is how
> I originally ran into the problem(s) that others had been
> reporting on the lists.)

buildworld buildkernel completed non-stop for the first time
on a BPI-M3 board.

Looks good for a check-in to svn to me (head and stable/11).

This combined with 2017-Feb-15's -r313772's fix to the fork
trampline code's updating of sp_el0 makes arm64 far more stable
for my purposes.

-r313772 was never MFC'd to stable/11. In my view it should be.

===
Mark Millard
markmi at dsl-only.net