From: Kristen Carlson Accardi <kris...@linux.intel.com> In cases EPC pages need be allocated during a page fault and the cgroup usage is near its limit, an asynchronous reclamation needs be triggered to avoid blocking the page fault handling.
Create a workqueue, corresponding work item and function definitions for EPC cgroup to support the asynchronous reclamation. In case the workqueue allocation is failed during init, disable cgroup. In sgx_cgroup_try_charge(), if caller does not allow synchronous reclamation, queue an asynchronous work into the workqueue. Co-developed-by: Sean Christopherson <sean.j.christopher...@intel.com> Signed-off-by: Sean Christopherson <sean.j.christopher...@intel.com> Signed-off-by: Kristen Carlson Accardi <kris...@linux.intel.com> Co-developed-by: Haitao Huang <haitao.hu...@linux.intel.com> Signed-off-by: Haitao Huang <haitao.hu...@linux.intel.com> --- V10: - Split asynchronous flow in separate patch. (Kai) - Consider cgroup disabled when the workqueue allocation fail during init. (Kai) - Abstract out sgx_cgroup_should_reclaim(). V9: - Add comments for static variables. (Jarkko) V8: - Remove alignment for substructure variables. (Jarkko) V7: - Split this out from the big patch, #10 in V6. (Dave, Kai) --- arch/x86/kernel/cpu/sgx/epc_cgroup.c | 134 ++++++++++++++++++++++++++- arch/x86/kernel/cpu/sgx/epc_cgroup.h | 1 + arch/x86/kernel/cpu/sgx/main.c | 8 +- 3 files changed, 135 insertions(+), 8 deletions(-) diff --git a/arch/x86/kernel/cpu/sgx/epc_cgroup.c b/arch/x86/kernel/cpu/sgx/epc_cgroup.c index f7a487a29ed1..3ca89b1fb7e2 100644 --- a/arch/x86/kernel/cpu/sgx/epc_cgroup.c +++ b/arch/x86/kernel/cpu/sgx/epc_cgroup.c @@ -5,9 +5,63 @@ #include <linux/kernel.h> #include "epc_cgroup.h" +/* + * The minimal free pages maintained by per-cgroup reclaimer + * Set this to the low threshold used by the global reclaimer, ksgxd. + */ +#define SGX_CG_MIN_FREE_PAGE (SGX_NR_LOW_PAGES) + +/* + * If the cgroup limit is close to SGX_CG_MIN_FREE_PAGE, maintaining the minimal + * free pages would barely leave any page for use, causing excessive reclamation + * and thrashing. + * + * Define the following limit, below which cgroup does not maintain the minimal + * free page threshold. Set this to quadruple of the minimal so at least 75% + * pages used without being reclaimed. + */ +#define SGX_CG_LOW_LIMIT (SGX_CG_MIN_FREE_PAGE * 4) + /* The root SGX EPC cgroup */ static struct sgx_cgroup sgx_cg_root; +/* + * The work queue that reclaims EPC pages in the background for cgroups. + * + * A cgroup schedules a work item into this queue to reclaim pages within the + * same cgroup when its usage limit is reached and synchronous reclamation is not + * an option, i.e., in a page fault handler. + */ +static struct workqueue_struct *sgx_cg_wq; + +static inline u64 sgx_cgroup_page_counter_read(struct sgx_cgroup *sgx_cg) +{ + return atomic64_read(&sgx_cg->cg->res[MISC_CG_RES_SGX_EPC].usage) / PAGE_SIZE; +} + +static inline u64 sgx_cgroup_max_pages(struct sgx_cgroup *sgx_cg) +{ + return READ_ONCE(sgx_cg->cg->res[MISC_CG_RES_SGX_EPC].max) / PAGE_SIZE; +} + +/* + * Get the lower bound of limits of a cgroup and its ancestors. Used in + * sgx_cgroup_should_reclaim() to determine if EPC usage of a cgroup is + * close to its limit or its ancestors' hence reclamation is needed. + */ +static inline u64 sgx_cgroup_max_pages_to_root(struct sgx_cgroup *sgx_cg) +{ + struct misc_cg *i = sgx_cg->cg; + u64 m = U64_MAX; + + while (i) { + m = min(m, READ_ONCE(i->res[MISC_CG_RES_SGX_EPC].max)); + i = misc_cg_parent(i); + } + + return m / PAGE_SIZE; +} + /** * sgx_cgroup_lru_empty() - check if a cgroup tree has no pages on its LRUs * @root: Root of the tree to check @@ -99,6 +153,61 @@ static void sgx_cgroup_reclaim_pages(struct misc_cg *root) rcu_read_unlock(); } +/** + * sgx_cgroup_should_reclaim() - check if EPC reclamation is needed for a cgroup + * @sgx_cg: The cgroup to be checked. + * + * This function can be used to guard a call to sgx_cgroup_reclaim_pages() where + * the minimal number of free page needs be maintained for the cgroup to make + * good forward progress. + * + * Return: %true if number of free pages available for the cgroup below a + * threshold (%SGX_CG_MIN_FREE_PAGE) and there are reclaimable pages within the + * cgroup. + */ +static bool sgx_cgroup_should_reclaim(struct sgx_cgroup *sgx_cg) +{ + u64 cur, max; + + if (sgx_cgroup_lru_empty(sgx_cg->cg)) + return false; + + max = sgx_cgroup_max_pages_to_root(sgx_cg); + + /* + * Unless the limit is very low, maintain a minimal number of free pages + * so there is always a few pages available to serve new allocation + * requests quickly. + */ + if (max > SGX_CG_LOW_LIMIT) + max -= SGX_CG_MIN_FREE_PAGE; + + cur = sgx_cgroup_page_counter_read(sgx_cg); + + return (cur >= max); +} + +/* + * Asynchronous work flow to reclaim pages from the cgroup when the cgroup is + * at/near its maximum capacity. + */ +static void sgx_cgroup_reclaim_work_func(struct work_struct *work) +{ + struct sgx_cgroup *sgx_cg = container_of(work, struct sgx_cgroup, reclaim_work); + + /* + * This work func is scheduled by sgx_cgroup_try_charge() when it cannot + * directly reclaim, i.e., EPC allocation in a fault handler. Waiting to + * reclaim until the cgroup is actually at its limit is less performant, + * as it means the task scheduling this asynchronous work is effectively + * blocked until a worker makes its way through the global work queue. + */ + while (sgx_cgroup_should_reclaim(sgx_cg)) { + sgx_cgroup_reclaim_pages(sgx_cg->cg); + cond_resched(); + } +} + static int __sgx_cgroup_try_charge(struct sgx_cgroup *epc_cg) { if (!misc_cg_try_charge(MISC_CG_RES_SGX_EPC, epc_cg->cg, PAGE_SIZE)) @@ -125,14 +234,24 @@ int sgx_cgroup_try_charge(struct sgx_cgroup *sgx_cg, enum sgx_reclaim reclaim) { int ret; + /* cgroup disabled due to wq allocation failure during sgx_cgroup_init(). */ + if (!sgx_cg_wq) + return 0; + + /* Should not happen if the wq is allocated and SGX cgroup initialized properly. */ + if (WARN_ON_ONCE(!sgx_cg)) + return 0; + for (;;) { ret = __sgx_cgroup_try_charge(sgx_cg); if (ret != -EBUSY) return ret; - if (reclaim == SGX_NO_RECLAIM) - return -ENOMEM; + if (reclaim == SGX_NO_RECLAIM) { + queue_work(sgx_cg_wq, &sgx_cg->reclaim_work); + return -EBUSY; + } sgx_cgroup_reclaim_pages(sgx_cg->cg); cond_resched(); @@ -147,7 +266,8 @@ int sgx_cgroup_try_charge(struct sgx_cgroup *sgx_cg, enum sgx_reclaim reclaim) */ void sgx_cgroup_uncharge(struct sgx_cgroup *sgx_cg) { - misc_cg_uncharge(MISC_CG_RES_SGX_EPC, sgx_cg->cg, PAGE_SIZE); + if (sgx_cg) + misc_cg_uncharge(MISC_CG_RES_SGX_EPC, sgx_cg->cg, PAGE_SIZE); } static void sgx_cgroup_free(struct misc_cg *cg) @@ -158,6 +278,7 @@ static void sgx_cgroup_free(struct misc_cg *cg) if (!sgx_cg) return; + cancel_work_sync(&sgx_cg->reclaim_work); kfree(sgx_cg); } @@ -171,6 +292,7 @@ const struct misc_res_ops sgx_cgroup_ops = { static void sgx_cgroup_misc_init(struct misc_cg *cg, struct sgx_cgroup *sgx_cg) { sgx_lru_init(&sgx_cg->lru); + INIT_WORK(&sgx_cg->reclaim_work, sgx_cgroup_reclaim_work_func); cg->res[MISC_CG_RES_SGX_EPC].priv = sgx_cg; sgx_cg->cg = cg; } @@ -190,6 +312,12 @@ static int sgx_cgroup_alloc(struct misc_cg *cg) void sgx_cgroup_init(void) { + sgx_cg_wq = alloc_workqueue("sgx_cg_wq", WQ_UNBOUND | WQ_FREEZABLE, WQ_UNBOUND_MAX_ACTIVE); + + /* All Cgroups functionalities are disabled. */ + if (WARN_ON(!sgx_cg_wq)) + return; + misc_cg_set_ops(MISC_CG_RES_SGX_EPC, &sgx_cgroup_ops); sgx_cgroup_misc_init(misc_cg_root(), &sgx_cg_root); } diff --git a/arch/x86/kernel/cpu/sgx/epc_cgroup.h b/arch/x86/kernel/cpu/sgx/epc_cgroup.h index f62dce0cac51..f66570d3ef42 100644 --- a/arch/x86/kernel/cpu/sgx/epc_cgroup.h +++ b/arch/x86/kernel/cpu/sgx/epc_cgroup.h @@ -32,6 +32,7 @@ static inline void sgx_cgroup_init(void) { } struct sgx_cgroup { struct misc_cg *cg; struct sgx_epc_lru_list lru; + struct work_struct reclaim_work; }; static inline struct sgx_cgroup *sgx_cgroup_from_misc_cg(struct misc_cg *cg) diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c index aaf341abc641..9f6594317ce4 100644 --- a/arch/x86/kernel/cpu/sgx/main.c +++ b/arch/x86/kernel/cpu/sgx/main.c @@ -650,11 +650,9 @@ void sgx_free_epc_page(struct sgx_epc_page *page) struct sgx_numa_node *node = section->node; #ifdef CONFIG_CGROUP_SGX_EPC - if (page->sgx_cg) { - sgx_cgroup_uncharge(page->sgx_cg); - sgx_put_cg(page->sgx_cg); - page->sgx_cg = NULL; - } + sgx_cgroup_uncharge(page->sgx_cg); + sgx_put_cg(page->sgx_cg); + page->sgx_cg = NULL; #endif spin_lock(&node->lock); -- 2.25.1