Re: [PATCH v10 12/14] x86/sgx: Turn on per-cgroup EPC reclamation

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On Mon, 08 Apr 2024 07:20:23 -0500, Huang, Kai <kai.huang@xxxxxxxxx> wrote:


--- a/arch/x86/kernel/cpu/sgx/epc_cgroup.h
+++ b/arch/x86/kernel/cpu/sgx/epc_cgroup.h
@@ -28,6 +28,10 @@ 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 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 {
 	struct misc_cg *cg;
@@ -65,6 +69,9 @@ 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);

Seems the decision to choose whether to implement a stub function for some
function is quite random to me.

My impression is people in general don't like #ifdef in the C file but prefer to
implementing it in the header in some helper function.

I guess you might want to just implement a stub function for each of the 3 functions exposed, so that we can eliminate some #ifdefs in the sgx/main.c (see
below).

 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 7f92455d957d..68f28ff2d5ef 100644
--- a/arch/x86/kernel/cpu/sgx/main.c
+++ b/arch/x86/kernel/cpu/sgx/main.c
@@ -34,6 +34,16 @@ static struct sgx_epc_lru_list sgx_global_lru;

static inline struct sgx_epc_lru_list *sgx_lru_list(struct sgx_epc_page *epc_page)
 {
+#ifdef CONFIG_CGROUP_SGX_EPC
+	if (epc_page->sgx_cg)
+		return &epc_page->sgx_cg->lru;
+
+	/*
+	 * This should not happen when cgroup is enabled: Every page belongs
+	 * to a cgroup, or the root by default.
+	 */
+	WARN_ON_ONCE(1);

In the case MISC cgroup is enabled in Kconfig but disabled by command line, I
think this becomes legal now?


I'm not sure actually. Never saw the warning even if I set "cgroup_disable=misc" in commandlibe. Tried both v1 and v2. Anyway, I think we can remove this warning and we handle the NULL sgx_cg now.

+#endif
 	return &sgx_global_lru;
 }

@@ -42,7 +52,11 @@ static inline struct sgx_epc_lru_list *sgx_lru_list(struct sgx_epc_page *epc_pag
  */
 static inline bool sgx_can_reclaim(void)
 {
+#ifdef CONFIG_CGROUP_SGX_EPC
+	return !sgx_cgroup_lru_empty(misc_cg_root());
+#else
 	return !list_empty(&sgx_global_lru.reclaimable);
+#endif
 }


Here you are using #ifdef  CONFIG_CGRUP_SGX_EPC, but ...

 static atomic_long_t sgx_nr_free_pages = ATOMIC_LONG_INIT(0);
@@ -404,7 +418,10 @@ 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);
 }

... here you are using IS_ENABLED(CONFIG_CGROUP_SGX_EPC).

Any reason they are not consistent?

I was hesitant to expose sgx_global_lru needed for implementing sgx_cgroup_lru_empty() stub which would also be a random decision and overkill to just remove couple of #ifdefs in short functions.


Also, in the case where MISC cgroup is disabled via commandline, I think it
won't work, because misc_cg_root() should be NULL in this case while
IS_ENABLED(CONFIG_CGROUP_SGX_EPC) is true.



The misc root cgroup is a static similar to sgx_cg_root. So misc_cg_root() won't be NULL However, based on how css_misc() was check NULL, I suppose sgx_get_current_cg() may be NULL when cgroup is disabled (again not 100% sure but we handle it anyway)

 /*
@@ -414,6 +431,16 @@ static void sgx_reclaim_pages_global(struct mm_struct *charge_mm)
  */
 void sgx_reclaim_direct(void)
 {
+#ifdef CONFIG_CGROUP_SGX_EPC
+	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(sgx_cg->cg, current->mm);
+		sgx_put_cg(sgx_cg);
+	}
+#endif

This #ifdef CONFIG_CGROUP_SGX_EPC can be removed if we implement a stub function
for sgx_cgroup_should_reclaim().

Yes.
+	/* Make sure there are some free pages at global level */
 	if (sgx_should_reclaim(SGX_NR_LOW_PAGES))
 		sgx_reclaim_pages_global(current->mm);
 }


Thanks
Haitao




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