[PATCH v11 12/14] x86/sgx: Turn on per-cgroup EPC reclamation

Haitao Huang
2024-04-10T18:26:07Z

From: Kristen Carlson Accardi <kristen@linux.intel.com>

Previous patches have implemented all infrastructure needed for
per-cgroup EPC page tracking and reclaiming. But all reclaimable EPC
pages are still tracked in the global LRU as sgx_lru_list() returns hard
coded reference to the global LRU.

Change sgx_lru_list() to return the LRU of the cgroup in which the given
EPC page is allocated.

This makes all EPC pages tracked in per-cgroup LRUs and the global
reclaimer (ksgxd) will not be able to reclaim any pages from the global
LRU. However, in cases of over-committing, i.e., the sum of cgroup
limits greater than the total capacity, cgroups may never reclaim but
the total usage can still be near the capacity. Therefore a global
reclamation is still needed in those cases and it should be performed
from the root cgroup.

Modify sgx_reclaim_pages_global(), to reclaim from the root EPC cgroup
when cgroup is enabled, otherwise from the global LRU. Export
sgx_cgroup_reclaim_pages() in the header file so it can be reused for
this purpose.

Similarly, modify sgx_can_reclaim(), to check emptiness of LRUs of all
cgroups when EPC cgroup is enabled, otherwise only check the global LRU.
Export sgx_cgroup_lru_empty() so it can be reused for this purpose.

Finally, change sgx_reclaim_direct(), to check and ensure there are free
pages at cgroup level so forward progress can be made by the caller.
Export sgx_cgroup_should_reclaim() for reuse.

With these changes, the global reclamation and per-cgroup reclamation
both work properly with all pages tracked in per-cgroup LRUs.

Co-developed-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Kristen Carlson Accardi <kristen@linux.intel.com>
Co-developed-by: Haitao Huang <haitao.huang@linux.intel.com>
Signed-off-by: Haitao Huang <haitao.huang@linux.intel.com>
---
V11:
- Reword the comments for global reclamation for allocation failure
after passing cgroup charging. (Kai)
- Add stub functions to remove ifdefs in c file (Kai)
- Add more detailed comments to clarify each page belongs to one cgroup, or the
root. (Kai)

V10:
- Add comment to clarify each page belongs to one cgroup, or the root by
default. (Kai)
- Merge the changes that expose sgx_cgroup_* functions to this patch.
- Add changes for sgx_reclaim_direct() that was missed previously.

V7:
- Split this out from the big patch, #10 in V6. (Dave, Kai)
---
arch/x86/kernel/cpu/sgx/epc_cgroup.c | 6 ++--
arch/x86/kernel/cpu/sgx/epc_cgroup.h | 27 +++++++++++++++++
arch/x86/kernel/cpu/sgx/main.c | 43 ++++++++++++++++++++++++++--
3 files changed, 71 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/sgx/epc_cgroup.c b/arch/x86/kernel/cpu/sgx/epc_cgroup.c
index 2efc33476b0b..16fe0e1574ec 100644
--- a/arch/x86/kernel/cpu/sgx/epc_cgroup.c
+++ b/arch/x86/kernel/cpu/sgx/epc_cgroup.c
@@ -68,7 +68,7 @@ static inline u64 sgx_cgroup_max_pages_to_root(struct sgx_cgroup *sgx_cg)
*
* Return: %true if all cgroups under the specified root have empty LRU lists.
*/
-static bool sgx_cgroup_lru_empty(struct misc_cg *root)
+bool sgx_cgroup_lru_empty(struct misc_cg *root)
{
struct cgroup_subsys_state *css_root;
struct cgroup_subsys_state *pos;
@@ -116,7 +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, struct mm_struct *charge_mm)
+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;
@@ -157,7 +157,7 @@ static void sgx_cgroup_reclaim_pages(struct misc_cg *root, struct mm_struct *cha
* 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)
+bool sgx_cgroup_should_reclaim(struct sgx_cgroup *sgx_cg)
{
u64 cur, max;

diff --git a/arch/x86/kernel/cpu/sgx/epc_cgroup.h b/arch/x86/kernel/cpu/sgx/epc_cgroup.h
index 9a2d51a91e5c..963aa19d3c47 100644
--- a/arch/x86/kernel/cpu/sgx/epc_cgroup.h
+++ b/arch/x86/kernel/cpu/sgx/epc_cgroup.h
@@ -13,6 +13,11 @@
#define MISC_CG_RES_SGX_EPC MISC_CG_RES_TYPES
struct sgx_cgroup;

+static inline struct misc_cg *misc_from_sgx(struct sgx_cgroup *sgx_cg)
+{
+ return NULL;
+}
+
static inline struct sgx_cgroup *sgx_get_current_cg(void)
{
return NULL;
@@ -27,8 +32,22 @@ static inline int sgx_cgroup_try_charge(struct sgx_cgroup *sgx_cg, enum sgx_recl

static inline void sgx_cgroup_uncharge(struct sgx_cgroup *sgx_cg) { }

+static inline bool sgx_cgroup_lru_empty(struct misc_cg *root)
+{
+ return true;
+}
+
+static inline bool sgx_cgroup_should_reclaim(struct sgx_cgroup *sgx_cg)
+{
+ return false;
+}
+
static inline void sgx_cgroup_init(void) { }

+static inline void sgx_cgroup_reclaim_pages(struct misc_cg *root, struct mm_struct *charge_mm)
+{
+}
+
#else

struct sgx_cgroup {
@@ -37,6 +56,11 @@ struct sgx_cgroup {
struct work_struct reclaim_work;
};

+static inline struct misc_cg *misc_from_sgx(struct sgx_cgroup *sgx_cg)
+{
+ return sgx_cg->cg;
+}
+
static inline struct sgx_cgroup *sgx_cgroup_from_misc_cg(struct misc_cg *cg)
{
return (struct sgx_cgroup *)(cg->res[MISC_CG_RES_SGX_EPC].priv);
@@ -67,6 +91,9 @@ static inline void sgx_put_cg(struct sgx_cgroup *sgx_cg)

int sgx_cgroup_try_charge(struct sgx_cgroup *sgx_cg, enum sgx_reclaim reclaim);
void sgx_cgroup_uncharge(struct sgx_cgroup *sgx_cg);
+bool sgx_cgroup_lru_empty(struct misc_cg *root);
+bool sgx_cgroup_should_reclaim(struct sgx_cgroup *sgx_cg);
+void sgx_cgroup_reclaim_pages(struct misc_cg *root, struct mm_struct *charge_mm);
void sgx_cgroup_init(void);

#endif
diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
index 11edbdb06782..e42e4a972752 100644
--- a/arch/x86/kernel/cpu/sgx/main.c
+++ b/arch/x86/kernel/cpu/sgx/main.c
@@ -32,9 +32,30 @@ static DEFINE_XARRAY(sgx_epc_address_space);
*/
static struct sgx_epc_lru_list sgx_global_lru;

+/*
+ * Get the per-cgroup or global LRU list that tracks the given reclaimable page.
+ */
static inline struct sgx_epc_lru_list *sgx_lru_list(struct sgx_epc_page *epc_page)
{
+#ifdef CONFIG_CGROUP_SGX_EPC
+ /*
+ * epc_page->sgx_cg here is never NULL during a reclaimable epc_page's
+ * life between sgx_alloc_epc_page() and sgx_free_epc_page():
+ *
+ * In sgx_alloc_epc_page(), epc_page->sgx_cg is set to the return from
+ * sgx_get_current_cg() which is the misc cgroup of the current task, or
+ * the root by default even if the misc cgroup is disabled by kernel
+ * command line.
+ *
+ * epc_page->sgx_cg is only unset by sgx_free_epc_page().
+ *
+ * This function is never used before sgx_alloc_epc_page() or after
+ * sgx_free_epc_page().
+ */
+ return &epc_page->sgx_cg->lru;
+#else
return &sgx_global_lru;
+#endif
}

/*
@@ -42,7 +63,8 @@ static inline struct sgx_epc_lru_list *sgx_lru_list(struct sgx_epc_page *epc_pag
*/
static inline bool sgx_can_reclaim(void)
{
- return !list_empty(&sgx_global_lru.reclaimable);
+ return !sgx_cgroup_lru_empty(misc_cg_root()) ||
+ !list_empty(&sgx_global_lru.reclaimable);
}

static atomic_long_t sgx_nr_free_pages = ATOMIC_LONG_INIT(0);
@@ -404,7 +426,10 @@ static bool sgx_should_reclaim(unsigned long watermark)

static void sgx_reclaim_pages_global(struct mm_struct *charge_mm)
{
- sgx_reclaim_pages(&sgx_global_lru, charge_mm);
+ if (IS_ENABLED(CONFIG_CGROUP_SGX_EPC))
+ sgx_cgroup_reclaim_pages(misc_cg_root(), charge_mm);
+ else
+ sgx_reclaim_pages(&sgx_global_lru, charge_mm);
}

/*
@@ -414,6 +439,14 @@ static void sgx_reclaim_pages_global(struct mm_struct *charge_mm)
*/
void sgx_reclaim_direct(void)
{
+ struct sgx_cgroup *sgx_cg = sgx_get_current_cg();
+
+ /* Make sure there are some free pages at cgroup level */
+ if (sgx_cg && sgx_cgroup_should_reclaim(sgx_cg)) {
+ sgx_cgroup_reclaim_pages(misc_from_sgx(sgx_cg), current->mm);
+ sgx_put_cg(sgx_cg);
+ }
+ /* Make sure there are some free pages at global level */
if (sgx_should_reclaim(SGX_NR_LOW_PAGES))
sgx_reclaim_pages_global(current->mm);
}
@@ -616,6 +649,12 @@ struct sgx_epc_page *sgx_alloc_epc_page(void *owner, enum sgx_reclaim reclaim)
break;
}

+ /*
+ * At this point, the usage within this cgroup is under its
+ * limit but there is no physical page left for allocation.
+ * Perform a global reclaim to get some pages released from any
+ * cgroup with reclaimable pages.
+ */
sgx_reclaim_pages_global(current->mm);
cond_resched();
}
--
2.25.1