[PATCH v11 10/14] x86/sgx: Charge mem_cgroup for per-cgroup reclamation

Haitao Huang
2024-04-10T18:26:05Z

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 considers all contexts other than the
ksgxd thread are user processes. 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.

Remove current_is_ksgxd() and change sgx_encl_get_mem_cgroup() to take
an additional argument to explicitly specify the mm struct to charge for
allocations. Callers from background kthreads not associated with a
charging mm struct would set it to NULL, while callers in user process
contexts set it to current->mm.

Internally, it handles the case when the charging mm given is NULL, by
searching for an mm struct from enclave's mm_list.

Signed-off-by: Haitao Huang <haitao.huang@linux.intel.com>
Reported-by: Mikko Ylinen <mikko.ylinen@linux.intel.com>
---
V10:
- Pass mm struct instead of a boolean 'indirect'. (Dave, Jarkko)

V9:
- Reduce number of if statements. (Tim)

V8:
- Limit text paragraphs to 80 characters wide. (Jarkko)
---
arch/x86/kernel/cpu/sgx/encl.c | 29 ++++++++++++++--------------
arch/x86/kernel/cpu/sgx/encl.h | 3 +--
arch/x86/kernel/cpu/sgx/epc_cgroup.c | 10 ++++++----
arch/x86/kernel/cpu/sgx/main.c | 29 +++++++++++++---------------
arch/x86/kernel/cpu/sgx/sgx.h | 2 +-
5 files changed, 36 insertions(+), 37 deletions(-)

diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c
index f474179b6f77..7b77dad41daf 100644
--- a/arch/x86/kernel/cpu/sgx/encl.c
+++ b/arch/x86/kernel/cpu/sgx/encl.c
@@ -993,23 +993,23 @@ 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.
+ * Find the mem_cgroup to charge for memory allocated on behalf of an enclave.
+ *
+ * Used in sgx_encl_alloc_backing() for backing store allocation.
+ *
+ * Return the mem_cgroup of the given charge_mm. Otherwise return 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)
+static struct mem_cgroup *sgx_encl_get_mem_cgroup(struct sgx_encl *encl,
+ struct mm_struct *charge_mm)
{
struct mem_cgroup *memcg = NULL;
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);
+ /* Use the charge_mm if given. */
+ if (charge_mm)
+ return get_mem_cgroup_from_mm(charge_mm);

/*
* Search the enclave's mm_list to find an mm associated with
@@ -1047,8 +1047,9 @@ 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
+ * @charge_mm: the mm to charge for the allocation
*
- * When called from ksgxd, sets the active memcg from one of the
+ * When charge_mm is NULL, 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
@@ -1060,9 +1061,9 @@ static struct mem_cgroup *sgx_encl_get_mem_cgroup(struct sgx_encl *encl)
* -errno otherwise.
*/
int sgx_encl_alloc_backing(struct sgx_encl *encl, unsigned long page_index,
- struct sgx_backing *backing)
+ struct sgx_backing *backing, struct mm_struct *charge_mm)
{
- struct mem_cgroup *encl_memcg = sgx_encl_get_mem_cgroup(encl);
+ struct mem_cgroup *encl_memcg = sgx_encl_get_mem_cgroup(encl, charge_mm);
struct mem_cgroup *memcg = set_active_memcg(encl_memcg);
int ret;

diff --git a/arch/x86/kernel/cpu/sgx/encl.h b/arch/x86/kernel/cpu/sgx/encl.h
index fe15ade02ca1..5ce9d108290f 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, struct mm_struct *charge_mm);
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 8151371a198b..2efc33476b0b 100644
--- a/arch/x86/kernel/cpu/sgx/epc_cgroup.c
+++ b/arch/x86/kernel/cpu/sgx/epc_cgroup.c
@@ -107,6 +107,7 @@ static bool sgx_cgroup_lru_empty(struct misc_cg *root)
/**
* sgx_cgroup_reclaim_pages() - reclaim EPC from a cgroup tree
* @root: The root of cgroup tree to reclaim from.
+ * @charge_mm: The mm to charge for backing store allocation.
*
* This function performs a pre-order walk in the cgroup tree under the given
* root, attempting to reclaim pages at each node until a fixed number of pages
@@ -115,7 +116,7 @@ static bool sgx_cgroup_lru_empty(struct misc_cg *root)
* the LRUs are recently accessed, i.e., considered "too young" to reclaim, no
* page will actually be reclaimed after walking the whole tree.
*/
-static void sgx_cgroup_reclaim_pages(struct misc_cg *root)
+static void sgx_cgroup_reclaim_pages(struct misc_cg *root, struct mm_struct *charge_mm)
{
struct cgroup_subsys_state *css_root;
struct cgroup_subsys_state *pos;
@@ -132,7 +133,7 @@ static void sgx_cgroup_reclaim_pages(struct misc_cg *root)
rcu_read_unlock();

sgx_cg = sgx_cgroup_from_misc_cg(css_misc(pos));
- cnt += sgx_reclaim_pages(&sgx_cg->lru);
+ cnt += sgx_reclaim_pages(&sgx_cg->lru, charge_mm);

rcu_read_lock();
css_put(pos);
@@ -194,7 +195,8 @@ static void sgx_cgroup_reclaim_work_func(struct work_struct *work)
* 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);
+ /* Indirect reclaim, no mm to charge, so NULL: */
+ sgx_cgroup_reclaim_pages(sgx_cg->cg, NULL);
cond_resched();
}
}
@@ -241,7 +243,7 @@ int sgx_cgroup_try_charge(struct sgx_cgroup *sgx_cg, enum sgx_reclaim reclaim)
return -EBUSY;
}

- sgx_cgroup_reclaim_pages(sgx_cg->cg);
+ sgx_cgroup_reclaim_pages(sgx_cg->cg, current->mm);
cond_resched();
}

diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
index b79c1d6cdc23..7f5428571c6a 100644
--- a/arch/x86/kernel/cpu/sgx/main.c
+++ b/arch/x86/kernel/cpu/sgx/main.c
@@ -253,8 +253,8 @@ 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)
+static void sgx_reclaimer_write(struct sgx_epc_page *epc_page, struct sgx_backing *backing,
+ struct mm_struct *charge_mm)
{
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, charge_mm);
if (ret)
goto out;

@@ -289,6 +289,7 @@ static void sgx_reclaimer_write(struct sgx_epc_page *epc_page,
/**
* sgx_reclaim_pages() - Attempt to reclaim a fixed number of pages from an LRU
* @lru: The LRU from which pages are reclaimed.
+ * @charge_mm: The mm to charge for backing store allocation.
*
* Take a fixed number of pages from the head of a given LRU and reclaim them to
* the enclave's private shmem files. Skip the pages, which have been accessed
@@ -304,7 +305,7 @@ static void sgx_reclaimer_write(struct sgx_epc_page *epc_page,
*
* Return: Number of pages attempted for reclamation.
*/
-unsigned int sgx_reclaim_pages(struct sgx_epc_lru_list *lru)
+unsigned int sgx_reclaim_pages(struct sgx_epc_lru_list *lru, struct mm_struct *charge_mm)
{
struct sgx_epc_page *chunk[SGX_NR_TO_SCAN];
struct sgx_backing backing[SGX_NR_TO_SCAN];
@@ -344,7 +345,7 @@ unsigned int sgx_reclaim_pages(struct sgx_epc_lru_list *lru)
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], charge_mm);
if (ret) {
mutex_unlock(&encl_page->encl->lock);
goto skip;
@@ -376,7 +377,7 @@ unsigned int sgx_reclaim_pages(struct sgx_epc_lru_list *lru)
continue;

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

kref_put(&encl_page->encl->refcount, sgx_encl_release);
epc_page->flags &= ~SGX_EPC_PAGE_RECLAIMER_TRACKED;
@@ -393,9 +394,9 @@ 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(struct mm_struct *charge_mm)
{
- sgx_reclaim_pages(&sgx_global_lru);
+ sgx_reclaim_pages(&sgx_global_lru, charge_mm);
}

/*
@@ -406,7 +407,7 @@ 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(current->mm);
}

static int ksgxd(void *p)
@@ -429,7 +430,8 @@ static int ksgxd(void *p)
sgx_should_reclaim(SGX_NR_HIGH_PAGES));

if (sgx_should_reclaim(SGX_NR_HIGH_PAGES))
- sgx_reclaim_pages_global();
+ /* Indirect reclaim, no mm to charge, so NULL: */
+ sgx_reclaim_pages_global(NULL);

cond_resched();
}
@@ -452,11 +454,6 @@ 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];
@@ -611,7 +608,7 @@ struct sgx_epc_page *sgx_alloc_epc_page(void *owner, enum sgx_reclaim reclaim)
break;
}

- sgx_reclaim_pages_global();
+ sgx_reclaim_pages_global(current->mm);
cond_resched();
}

diff --git a/arch/x86/kernel/cpu/sgx/sgx.h b/arch/x86/kernel/cpu/sgx/sgx.h
index 828d30cd18fa..7460c4d9d1e9 100644
--- a/arch/x86/kernel/cpu/sgx/sgx.h
+++ b/arch/x86/kernel/cpu/sgx/sgx.h
@@ -135,7 +135,7 @@ 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, enum sgx_reclaim reclaim);
-unsigned int sgx_reclaim_pages(struct sgx_epc_lru_list *lru);
+unsigned int sgx_reclaim_pages(struct sgx_epc_lru_list *lru, struct mm_struct *charge_mm);

void sgx_ipi_cb(void *info);

--
2.25.1