Re: [PATCH v5 16/18] x86/sgx: Limit process EPC usage with misc cgroup controller

Huang, Kai
2023-10-10T00:26:08Z

> @@ -332,6 +336,7 @@ void sgx_isolate_epc_pages(struct sgx_epc_lru_lists *lru, size_t nr_to_scan,
> * sgx_reclaim_epc_pages() - Reclaim EPC pages from the consumers
> * @nr_to_scan: Number of EPC pages to scan for reclaim
> * @ignore_age: Reclaim a page even if it is young
> + * @epc_cg: EPC cgroup from which to reclaim
> *
> * Take a fixed number of pages from the head of the active page pool and
> * reclaim them to the enclave's private shmem files. Skip the pages, which have
> @@ -345,7 +350,8 @@ void sgx_isolate_epc_pages(struct sgx_epc_lru_lists *lru, size_t nr_to_scan,
> * problematic as it would increase the lock contention too much, which would
> * halt forward progress.
> */
> -size_t sgx_reclaim_epc_pages(size_t nr_to_scan, bool ignore_age)
> +size_t sgx_reclaim_epc_pages(size_t nr_to_scan, bool ignore_age,
> + struct sgx_epc_cgroup *epc_cg)
> {
> struct sgx_backing backing[SGX_NR_TO_SCAN_MAX];
> struct sgx_epc_page *epc_page, *tmp;
> @@ -355,7 +361,15 @@ size_t sgx_reclaim_epc_pages(size_t nr_to_scan, bool ignore_age)
> LIST_HEAD(iso);
> size_t ret, i;
>
> - sgx_isolate_epc_pages(&sgx_global_lru, nr_to_scan, &iso);
> + /*
> + * If a specific cgroup is not being targeted, take from the global
> + * list first, even when cgroups are enabled. If there are
> + * pages on the global LRU then they should get reclaimed asap.
> + */
> + if (!IS_ENABLED(CONFIG_CGROUP_SGX_EPC) || !epc_cg)
> + sgx_isolate_epc_pages(&sgx_global_lru, &nr_to_scan, &iso);
> +
> + sgx_epc_cgroup_isolate_pages(epc_cg, &nr_to_scan, &iso);

(I wish such code can be somehow moved to the earlier patches, so that we can
get early idea that how sgx_reclaim_epc_pages() is supposed to be used.)

So here when we are not targeting a specific EPC cgroup, we always reclaim from
the global list first, ...

[...]

>
> if (list_empty(&iso))
> return 0;
> @@ -423,7 +437,7 @@ static bool sgx_should_reclaim(unsigned long watermark)
> void sgx_reclaim_direct(void)
> {
> if (sgx_should_reclaim(SGX_NR_LOW_PAGES))
> - sgx_reclaim_epc_pages(SGX_NR_TO_SCAN, false);
> + sgx_reclaim_epc_pages(SGX_NR_TO_SCAN, false, NULL);

... and we always try to reclaim the global list first when directly reclaim is
desired, even the enclave is within some EPC cgroup. ...

> }
>
> static int ksgxd(void *p)
> @@ -446,7 +460,7 @@ static int ksgxd(void *p)
> sgx_should_reclaim(SGX_NR_HIGH_PAGES));
>
> if (sgx_should_reclaim(SGX_NR_HIGH_PAGES))
> - sgx_reclaim_epc_pages(SGX_NR_TO_SCAN, false);
> + sgx_reclaim_epc_pages(SGX_NR_TO_SCAN, false, NULL);

... and in ksgxd() as well, which I guess is somehow acceptable. ...

>
> cond_resched();
> }
> @@ -600,6 +614,11 @@ int sgx_drop_epc_page(struct sgx_epc_page *page)
> struct sgx_epc_page *sgx_alloc_epc_page(void *owner, bool reclaim)
> {
> struct sgx_epc_page *page;
> + struct sgx_epc_cgroup *epc_cg;
> +
> + epc_cg = sgx_epc_cgroup_try_charge(reclaim);
> + if (IS_ERR(epc_cg))
> + return ERR_CAST(epc_cg);
>
> for ( ; ; ) {
> page = __sgx_alloc_epc_page();
> @@ -608,8 +627,10 @@ struct sgx_epc_page *sgx_alloc_epc_page(void *owner, bool reclaim)
> break;
> }
>
> - if (!sgx_can_reclaim())
> - return ERR_PTR(-ENOMEM);
> + if (!sgx_can_reclaim()) {
> + page = ERR_PTR(-ENOMEM);
> + break;
> + }
>
> if (!reclaim) {
> page = ERR_PTR(-EBUSY);
> @@ -621,10 +642,17 @@ struct sgx_epc_page *sgx_alloc_epc_page(void *owner, bool reclaim)
> break;
> }
>
> - sgx_reclaim_epc_pages(SGX_NR_TO_SCAN, false);
> + sgx_reclaim_epc_pages(SGX_NR_TO_SCAN, false, NULL);

... and when an EPC page is allocated, no matter whether the EPC page belongs to
any cgroup or not.

When we are allocating EPC page for one enclave, if that enclave belongs to some
cgroup, is it more reasonable to reclaim EPC pages from it's own group (and the
children under it)?

You already got the current EPC cgroup at the beginning of sgx_alloc_epc_page()
when you want to charge the EPC allocation.

> cond_resched();
> }
>