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

Haitao Huang
2024-02-05T21:06:47Z

Enclave Page Cache(EPC) memory can be swapped out to regular system
memory, and the consumed memory should be charged to a proper
mem_cgroup. Currently the selection of mem_cgroup to charge is done in
sgx_encl_get_mem_cgroup(). But it only considers two contexts in which
the swapping can be done: normal tasks and the ksgxd kthread.
With the new EPC cgroup implementation, the swapping can also happen in
EPC cgroup work-queue threads. In those cases, it improperly selects the
root mem_cgroup to charge for the RAM usage.

Change sgx_encl_get_mem_cgroup() to handle non-task contexts only and
return the mem_cgroup of an mm_struct associated with the enclave. The
return is used to charge for EPC backing pages in all kthread cases.

Pass a flag into the top level reclamation function,
sgx_reclaim_pages(), to explicitly indicate whether it is called from a
background kthread. Internally, if the flag is true, switch the active
mem_cgroup to the one returned from sgx_encl_get_mem_cgroup(), prior to
any backing page allocation, in order to ensure that shmem page
allocations are charged to the enclave's cgroup.

Removed current_is_ksgxd() as it is no longer needed.

Signed-off-by: Haitao Huang <haitao.huang@linux.intel.com>
Reported-by: Mikko Ylinen <mikko.ylinen@linux.intel.com>
---
V9:
- Reduce number of if statements. (Tim)

V8:
- Limit text paragraphs to 80 characters wide. (Jarkko)
---
arch/x86/kernel/cpu/sgx/encl.c | 38 +++++++++++++---------------
arch/x86/kernel/cpu/sgx/encl.h | 3 +--
arch/x86/kernel/cpu/sgx/epc_cgroup.c | 7 ++---
arch/x86/kernel/cpu/sgx/main.c | 27 +++++++++-----------
arch/x86/kernel/cpu/sgx/sgx.h | 3 ++-
5 files changed, 36 insertions(+), 42 deletions(-)

diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c
index 279148e72459..4e5948362060 100644
--- a/arch/x86/kernel/cpu/sgx/encl.c
+++ b/arch/x86/kernel/cpu/sgx/encl.c
@@ -993,9 +993,7 @@ static int __sgx_encl_get_backing(struct sgx_encl *encl, unsigned long page_inde
}

/*
- * When called from ksgxd, returns the mem_cgroup of a struct mm stored
- * in the enclave's mm_list. When not called from ksgxd, just returns
- * the mem_cgroup of the current task.
+ * Returns the mem_cgroup of a struct mm stored in the enclave's mm_list.
*/
static struct mem_cgroup *sgx_encl_get_mem_cgroup(struct sgx_encl *encl)
{
@@ -1003,14 +1001,6 @@ static struct mem_cgroup *sgx_encl_get_mem_cgroup(struct sgx_encl *encl)
struct sgx_encl_mm *encl_mm;
int idx;

- /*
- * If called from normal task context, return the mem_cgroup
- * of the current task's mm. The remainder of the handling is for
- * ksgxd.
- */
- if (!current_is_ksgxd())
- return get_mem_cgroup_from_mm(current->mm);
-
/*
* Search the enclave's mm_list to find an mm associated with
* this enclave to charge the allocation to.
@@ -1047,27 +1037,33 @@ static struct mem_cgroup *sgx_encl_get_mem_cgroup(struct sgx_encl *encl)
* @encl: an enclave pointer
* @page_index: enclave page index
* @backing: data for accessing backing storage for the page
+ * @indirect: in ksgxd or EPC cgroup work queue context
+ *
+ * Create a backing page for loading data back into an EPC page with ELDU. This
+ * function takes a reference on a new backing page which must be dropped with a
+ * corresponding call to sgx_encl_put_backing().
*
- * When called from ksgxd, sets the active memcg from one of the
- * mms in the enclave's mm_list prior to any backing page allocation,
- * in order to ensure that shmem page allocations are charged to the
- * enclave. Create a backing page for loading data back into an EPC page with
- * ELDU. This function takes a reference on a new backing page which
- * must be dropped with a corresponding call to sgx_encl_put_backing().
+ * When @indirect is true, sets the active memcg from one of the mms in the
+ * enclave's mm_list prior to any backing page allocation, in order to ensure
+ * that shmem page allocations are charged to the enclave.
*
* Return:
* 0 on success,
* -errno otherwise.
*/
int sgx_encl_alloc_backing(struct sgx_encl *encl, unsigned long page_index,
- struct sgx_backing *backing)
+ struct sgx_backing *backing, bool indirect)
{
- 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);

+ encl_memcg = sgx_encl_get_mem_cgroup(encl);
+ memcg = set_active_memcg(encl_memcg);
+ ret = __sgx_encl_get_backing(encl, page_index, backing);
set_active_memcg(memcg);
mem_cgroup_put(encl_memcg);

diff --git a/arch/x86/kernel/cpu/sgx/encl.h b/arch/x86/kernel/cpu/sgx/encl.h
index f94ff14c9486..549cd2e8d98b 100644
--- a/arch/x86/kernel/cpu/sgx/encl.h
+++ b/arch/x86/kernel/cpu/sgx/encl.h
@@ -103,12 +103,11 @@ static inline int sgx_encl_find(struct mm_struct *mm, unsigned long addr,
int sgx_encl_may_map(struct sgx_encl *encl, unsigned long start,
unsigned long end, unsigned long vm_flags);

-bool current_is_ksgxd(void);
void sgx_encl_release(struct kref *ref);
int sgx_encl_mm_add(struct sgx_encl *encl, struct mm_struct *mm);
const cpumask_t *sgx_encl_cpumask(struct sgx_encl *encl);
int sgx_encl_alloc_backing(struct sgx_encl *encl, unsigned long page_index,
- struct sgx_backing *backing);
+ struct sgx_backing *backing, bool indirect);
void sgx_encl_put_backing(struct sgx_backing *backing);
int sgx_encl_test_and_clear_young(struct mm_struct *mm,
struct sgx_encl_page *page);
diff --git a/arch/x86/kernel/cpu/sgx/epc_cgroup.c b/arch/x86/kernel/cpu/sgx/epc_cgroup.c
index 16b6d9f909eb..d399fda2b55e 100644
--- a/arch/x86/kernel/cpu/sgx/epc_cgroup.c
+++ b/arch/x86/kernel/cpu/sgx/epc_cgroup.c
@@ -93,9 +93,10 @@ bool sgx_epc_cgroup_lru_empty(struct misc_cg *root)
/**
* sgx_epc_cgroup_reclaim_pages() - walk a cgroup tree and scan LRUs to reclaim pages
* @root: Root of the tree to start walking from.
+ * @indirect: In ksgxd or EPC cgroup work queue context.
* Return: Number of pages reclaimed.
*/
-unsigned int sgx_epc_cgroup_reclaim_pages(struct misc_cg *root)
+static unsigned int sgx_epc_cgroup_reclaim_pages(struct misc_cg *root, bool indirect)
{
/*
* Attempting to reclaim only a few pages will often fail and is
@@ -119,7 +120,7 @@ unsigned int sgx_epc_cgroup_reclaim_pages(struct misc_cg *root)
rcu_read_unlock();

epc_cg = sgx_epc_cgroup_from_misc_cg(css_misc(pos));
- cnt += sgx_reclaim_pages(&epc_cg->lru, &nr_to_scan);
+ cnt += sgx_reclaim_pages(&epc_cg->lru, &nr_to_scan, indirect);

rcu_read_lock();
css_put(pos);
@@ -176,7 +177,7 @@ static void sgx_epc_cgroup_reclaim_work_func(struct work_struct *work)
break;

/* Keep reclaiming until above condition is met. */
- sgx_epc_cgroup_reclaim_pages(epc_cg->cg);
+ sgx_epc_cgroup_reclaim_pages(epc_cg->cg, true);
}
}

diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
index 4f5824c4751d..51904f191b97 100644
--- a/arch/x86/kernel/cpu/sgx/main.c
+++ b/arch/x86/kernel/cpu/sgx/main.c
@@ -254,7 +254,7 @@ static void sgx_encl_ewb(struct sgx_epc_page *epc_page,
}

static void sgx_reclaimer_write(struct sgx_epc_page *epc_page,
- struct sgx_backing *backing)
+ struct sgx_backing *backing, bool indirect)
{
struct sgx_encl_page *encl_page = epc_page->owner;
struct sgx_encl *encl = encl_page->encl;
@@ -270,7 +270,7 @@ static void sgx_reclaimer_write(struct sgx_epc_page *epc_page,

if (!encl->secs_child_cnt && test_bit(SGX_ENCL_INITIALIZED, &encl->flags)) {
ret = sgx_encl_alloc_backing(encl, PFN_DOWN(encl->size),
- &secs_backing);
+ &secs_backing, indirect);
if (ret)
goto out;

@@ -304,9 +304,11 @@ static void sgx_reclaimer_write(struct sgx_epc_page *epc_page,
* @lru: The LRU from which pages are reclaimed.
* @nr_to_scan: Pointer to the target number of pages to scan, must be less than
* SGX_NR_TO_SCAN.
+ * @indirect: In ksgxd or EPC cgroup work queue contexts.
* Return: Number of pages reclaimed.
*/
-unsigned int sgx_reclaim_pages(struct sgx_epc_lru_list *lru, unsigned int *nr_to_scan)
+unsigned int sgx_reclaim_pages(struct sgx_epc_lru_list *lru, unsigned int *nr_to_scan,
+ bool indirect)
{
struct sgx_epc_page *chunk[SGX_NR_TO_SCAN];
struct sgx_backing backing[SGX_NR_TO_SCAN];
@@ -348,7 +350,7 @@ unsigned int sgx_reclaim_pages(struct sgx_epc_lru_list *lru, unsigned int *nr_to
page_index = PFN_DOWN(encl_page->desc - encl_page->encl->base);

mutex_lock(&encl_page->encl->lock);
- ret = sgx_encl_alloc_backing(encl_page->encl, page_index, &backing[i]);
+ ret = sgx_encl_alloc_backing(encl_page->encl, page_index, &backing[i], indirect);
if (ret) {
mutex_unlock(&encl_page->encl->lock);
goto skip;
@@ -381,7 +383,7 @@ unsigned int sgx_reclaim_pages(struct sgx_epc_lru_list *lru, unsigned int *nr_to
continue;

encl_page = epc_page->owner;
- sgx_reclaimer_write(epc_page, &backing[i]);
+ sgx_reclaimer_write(epc_page, &backing[i], indirect);

kref_put(&encl_page->encl->refcount, sgx_encl_release);
epc_page->flags &= ~SGX_EPC_PAGE_RECLAIMER_TRACKED;
@@ -399,11 +401,11 @@ static bool sgx_should_reclaim(unsigned long watermark)
!list_empty(&sgx_global_lru.reclaimable);
}

-static void sgx_reclaim_pages_global(void)
+static void sgx_reclaim_pages_global(bool indirect)
{
unsigned int nr_to_scan = SGX_NR_TO_SCAN;

- sgx_reclaim_pages(&sgx_global_lru, &nr_to_scan);
+ sgx_reclaim_pages(&sgx_global_lru, &nr_to_scan, indirect);
}

/*
@@ -414,7 +416,7 @@ static void sgx_reclaim_pages_global(void)
void sgx_reclaim_direct(void)
{
if (sgx_should_reclaim(SGX_NR_LOW_PAGES))
- sgx_reclaim_pages_global();
+ sgx_reclaim_pages_global(false);
}

static int ksgxd(void *p)
@@ -437,7 +439,7 @@ static int ksgxd(void *p)
sgx_should_reclaim(SGX_NR_HIGH_PAGES));

if (sgx_should_reclaim(SGX_NR_HIGH_PAGES))
- sgx_reclaim_pages_global();
+ sgx_reclaim_pages_global(true);

cond_resched();
}
@@ -460,11 +462,6 @@ static bool __init sgx_page_reclaimer_init(void)
return true;
}

-bool current_is_ksgxd(void)
-{
- return current == ksgxd_tsk;
-}
-
static struct sgx_epc_page *__sgx_alloc_epc_page_from_node(int nid)
{
struct sgx_numa_node *node = &sgx_numa_nodes[nid];
@@ -623,7 +620,7 @@ struct sgx_epc_page *sgx_alloc_epc_page(void *owner, bool reclaim)
* Need to do a global reclamation if cgroup was not full but free
* physical pages run out, causing __sgx_alloc_epc_page() to fail.
*/
- sgx_reclaim_pages_global();
+ sgx_reclaim_pages_global(false);
cond_resched();
}

diff --git a/arch/x86/kernel/cpu/sgx/sgx.h b/arch/x86/kernel/cpu/sgx/sgx.h
index 2593c013d091..cfe906054d85 100644
--- a/arch/x86/kernel/cpu/sgx/sgx.h
+++ b/arch/x86/kernel/cpu/sgx/sgx.h
@@ -110,7 +110,8 @@ void sgx_reclaim_direct(void);
void sgx_mark_page_reclaimable(struct sgx_epc_page *page);
int sgx_unmark_page_reclaimable(struct sgx_epc_page *page);
struct sgx_epc_page *sgx_alloc_epc_page(void *owner, bool reclaim);
-unsigned int sgx_reclaim_pages(struct sgx_epc_lru_list *lru, unsigned int *nr_to_scan);
+unsigned int sgx_reclaim_pages(struct sgx_epc_lru_list *lru, unsigned int *nr_to_scan,
+ bool indirect);

void sgx_ipi_cb(void *info);

--
2.25.1