From: Kristen Carlson Accardi
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
Signed-off-by: Sean Christopherson
Signed-off-by: Kristen Carlson Accardi
Co-developed-by: Haitao Huang
Signed-off-by: Haitao Huang
---
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
#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(_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
