On Thu, 2022-03-31 at 00:46 +0000, Song Liu wrote:

quoted

On Mar 30, 2022, at 5:04 PM, Edgecombe, Rick P <
rick.p.edgecombe@intel.com> wrote:

On Wed, 2022-03-30 at 15:56 -0700, Song Liu wrote:

quoted

[1] 

https://lore.kernel.org/lkml/5bd16e2c06a2df357400556c6ae01bb5d3c5c32a.camel@intel.com/ (local)

quoted

The issues I brought up around VM_FLUSH_RESET_PERMS are not fixed
in
this series. And I think the solution I proposed is kind of wonky
with
respect to hibernate. So I think maybe hibernate should be fixed to
not
impose restrictions on the direct map, so the wonkiness is not
needed.
But then this "fixes" series becomes quite extensive.

I wonder, why not just push the patch 1 here, then re-enable this
thing
when it is all properly fixed up. It looked like your code could
handle
the allocation not actually getting large pages.

Only shipping patch 1 should eliminate the issues. But that will also
reduce the benefit in iTLB efficiency (I don't know by how much yet.)

Yea, it's just a matter of what order/timeline things get done in. This
change didn't get enough mm attention ahead of time. Now there are two
issues. One where the root cause is not fully clear and one that
properly needs a wider fix. Just thinking it could be nice to take some
time on it, rather than rush to finish what was already too rushed.

quoted

Another solution that would keep large pages but still need fixing
up
later: Just don't use VM_FLUSH_RESET_PERMS for now. Call
set_memory_nx() and then set_memory_rw() on the module space
address
before vfree(). This will clean up everything that's needed with
respect to direct map permissions. Have vmalloc warn if is sees
VM_FLUSH_RESET_PERMS and huge pages together.

Do you mean we should remove set_vm_flush_reset_perms() from 
alloc_new_pack() and do set_memory_nx() and set_memory_rw() before
we call vfree() in bpf_prog_pack_free()? If this works, I would
prefer
we go with this way. 

I believe this would work functionally.