Re: [PATCH bpf 0/4] introduce HAVE_ARCH_HUGE_VMALLOC_FLAG for bpf_prog_pack

[Song Liu <songliubraving@fb.com>]

> 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:
>> [1] 
>> https://lore.kernel.org/lkml/5bd16e2c06a2df357400556c6ae01bb5d3c5c32a.camel@intel.com/
> 
> 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.)

> 
> 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. 

Thanks,
Song