Re: [PATCH v9 09/15] x86/sgx: Charge mem_cgroup for per-cgroup reclamation

Haitao Huang
2024-02-13T03:21:51Z

On Mon, 12 Feb 2024 13:46:06 -0600, Jarkko Sakkinen <jarkko@kernel.org>
wrote:

> On Mon Feb 5, 2024 at 11:06 PM EET, Haitao Huang wrote:
>> Enclave Page Cache(EPC) memory can be swapped out to regular system
>
> "Enclave Page Cache (EPC)"
> ~
>
Will fix.

[...]
>> int sgx_encl_alloc_backing(struct sgx_encl *encl, unsigned long
>> page_index,
>> - struct sgx_backing *backing)
>> + struct sgx_backing *backing, bool indirect)
>
> Boolean parameters should be avoided when possible because they confuse
> in the call sites.
>
>> {
>> - struct mem_cgroup *encl_memcg = sgx_encl_get_mem_cgroup(encl);
>> - struct mem_cgroup *memcg = set_active_memcg(encl_memcg);
>> + struct mem_cgroup *encl_memcg;
>> + struct mem_cgroup *memcg;
>> int ret;
>>
>> - ret = __sgx_encl_get_backing(encl, page_index, backing);
>> + if (!indirect)
>> + return __sgx_encl_get_backing(encl, page_index, backing);
>
> If a call is either in heead or tail of the code block, then
> obviously better option is to make __sgx_encl_get_backing()
> as non-static sgx_encl_get_backing() and call it in those
> call sites that would call this with "false".
>
> I.e. you need a new patch where this preparation is done.
>

This would actually require more intrusive changes to the call stack for
global and cgroup reclaim:

{sgx_epc_cgroup_reclaim_pages(),sgx_reclaim_pages_global()}->sgx_reclaim_pages()[->sgx_reclaimer_write()]->sgx_encl_alloc_backing()

We need make two versions of each of those functions.
It'd be especially complicated in refactoring sgx_reclaim_pages() for two
versions.

I now double checked the history of current_is_ksgxd()[1], it seemed the
intent was to replace "current->mm == NULL" criteria so it is more obvious
we are running in ksgxd.

@Dave, @Kristen,

Can we restore the original criteria like below so it works for the cgroup
work-queues?

bool current_is_ksgxd(void)
{
return current == ksgxd_tsk;
}

--->

bool current_is_kthread(void)
{
return current->mm == NULL;
}

I'm not experienced in this area and not sure how reliable it is to use
current->mm == NULL for kthread and work-queues. But it would eliminate
the need for the boolean parameter.

Would appreciate the input.

Haitao

[1]https://lore.kernel.org/linux-sgx/9c269c70-35fe-a1a4-34c9-b1e62ab3bb3b@intel.com/