[PATCH v4 3/3] x86/sgx: Add a basic NUMA allocation scheme to sgx_alloc_epc_page()

[Jarkko Sakkinen]

Background
==========

EPC section is covered by one or more SRAT entries that are associated with
one and only one PXM (NUMA node). The motivation behind this patch is to
provide basic elements of building allocation scheme based on this premise.

Just like normal RAM, enclave memory (EPC) should be covered by entries
in the ACPI SRAT table.  These entries allow each EPC section to be
associated with a NUMA node.

Use this information to implement a simple NUMA-aware allocator for
enclave memory.

Solution
========

Use phys_to_target_node() to associate each NUMA node with the EPC
sections contained within its range. In sgx_alloc_epc_page(), first try
to allocate from the NUMA node, where the CPU is executing. If that
fails, allocate from other nodes, iterating them from the current node
in order.

Other
=====

NUMA_KEEP_MEMINFO dependency is required for phys_to_target_node().

Link: https://lore.kernel.org/lkml/158188326978.894464.217282995221175417.stgit@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
Signed-off-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx>
---

v4:
* Cycle nodes instead of a global page list, starting from the node
  of the current thread.
* Documented NUMA_KEEP_MEMINFO dependency to the commit message.
* Added NUMA node pointer to struct sgx_epc_section. EPC page should
  reference to a section, since potentially a node could have multiple
  sections (Intel SDM does not say anything explicit about this).
  This the safest play.
* Remove nodes_clear(sgx_numa_node_mask).
* Appended Dave's additions to the commit message for the background
  section.

 arch/x86/Kconfig               |   1 +
 arch/x86/kernel/cpu/sgx/main.c | 117 ++++++++++++++++++++-------------
 arch/x86/kernel/cpu/sgx/sgx.h  |  16 +++--
 3 files changed, 84 insertions(+), 50 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 513895af8ee7..3e6152a8dd2b 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1930,6 +1930,7 @@ config X86_SGX
 	depends on CRYPTO_SHA256=y
 	select SRCU
 	select MMU_NOTIFIER
+	select NUMA_KEEP_MEMINFO if NUMA
 	help
 	  Intel(R) Software Guard eXtensions (SGX) is a set of CPU instructions
 	  that can be used by applications to set aside private regions of code
diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
index cb4561444b96..3b524a1361d6 100644
--- a/arch/x86/kernel/cpu/sgx/main.c
+++ b/arch/x86/kernel/cpu/sgx/main.c
@@ -18,14 +18,23 @@ static int sgx_nr_epc_sections;
 static struct task_struct *ksgxd_tsk;
 static DECLARE_WAIT_QUEUE_HEAD(ksgxd_waitq);
 
-/*
- * These variables are part of the state of the reclaimer, and must be accessed
- * with sgx_reclaimer_lock acquired.
- */
+/* The reclaimer lock protected variables prepend the lock. */
 static LIST_HEAD(sgx_active_page_list);
-
 static DEFINE_SPINLOCK(sgx_reclaimer_lock);
 
+/* The free page list lock protected variables prepend the lock. */
+static unsigned long sgx_nr_free_pages;
+
+/* Nodes with one or more EPC sections. */
+static nodemask_t sgx_numa_mask;
+
+/*
+ * Array with one list_head for each possible NUMA node.  Each
+ * list contains all the sgx_epc_section's which are on that
+ * node.
+ */
+static struct sgx_numa_node *sgx_numa_nodes;
+
 /*
  * When the driver initialized, EPC pages go first here, as they could be
  * initialized to an active enclave, on kexec entry.
@@ -352,21 +361,9 @@ static void sgx_reclaim_pages(void)
 	}
 }
 
-static unsigned long sgx_nr_free_pages(void)
-{
-	unsigned long cnt = 0;
-	int i;
-
-	for (i = 0; i < sgx_nr_epc_sections; i++)
-		cnt += sgx_epc_sections[i].free_cnt;
-
-	return cnt;
-}
-
 static bool sgx_should_reclaim(unsigned long watermark)
 {
-	return sgx_nr_free_pages() < watermark &&
-	       !list_empty(&sgx_active_page_list);
+	return sgx_nr_free_pages < watermark && !list_empty(&sgx_active_page_list);
 }
 
 static int ksgxd(void *p)
@@ -443,50 +440,63 @@ static bool __init sgx_page_reclaimer_init(void)
 	return true;
 }
 
-static struct sgx_epc_page *__sgx_alloc_epc_page_from_section(struct sgx_epc_section *section)
+static struct sgx_epc_page *__sgx_alloc_epc_page_from_node(int nid)
 {
-	struct sgx_epc_page *page;
+	struct sgx_numa_node *node = &sgx_numa_nodes[nid];
+	struct sgx_epc_page *page = NULL;
+
+	if (!node_isset(nid, sgx_numa_mask))
+		return NULL;
 
-	spin_lock(&section->lock);
+	spin_lock(&node->lock);
 
-	if (list_empty(&section->page_list)) {
-		spin_unlock(&section->lock);
+	if (list_empty(&node->free_page_list)) {
+		spin_unlock(&node->lock);
 		return NULL;
 	}
 
-	page = list_first_entry(&section->page_list, struct sgx_epc_page, list);
+	page = list_first_entry(&node->free_page_list, struct sgx_epc_page, list);
 	list_del_init(&page->list);
-	section->free_cnt--;
+	sgx_nr_free_pages--;
+
+	spin_unlock(&node->lock);
 
-	spin_unlock(&section->lock);
 	return page;
 }
 
 /**
  * __sgx_alloc_epc_page() - Allocate an EPC page
  *
- * Iterate through EPC sections and borrow a free EPC page to the caller. When a
- * page is no longer needed it must be released with sgx_free_epc_page().
+ * Iterate through NUMA nodes and borrow a free EPC page to the caller. When a
+ * page is no longer needed it must be released with sgx_free_epc_page(). Start
+ * from the NUMA node, where the caller is executing.
  *
  * Return:
- *   an EPC page,
- *   -errno on error
+ * - an EPC page:	Free EPC pages were available.
+ * - ERR_PTR(-ENOMEM):	Run out of EPC pages.
  */
 struct sgx_epc_page *__sgx_alloc_epc_page(void)
 {
-	struct sgx_epc_section *section;
 	struct sgx_epc_page *page;
-	int i;
+	int nid = numa_node_id();
 
-	for (i = 0; i < sgx_nr_epc_sections; i++) {
-		section = &sgx_epc_sections[i];
+	/* Try to allocate EPC from the current node, first: */
+	page = __sgx_alloc_epc_page_from_node(nid);
+	if (page)
+		return page;
 
-		page = __sgx_alloc_epc_page_from_section(section);
+	/* Then, go through the other nodes: */
+	while (true) {
+		nid = next_node_in(nid, sgx_numa_mask);
+		if (nid == numa_node_id())
+			break;
+
+		page = __sgx_alloc_epc_page_from_node(nid);
 		if (page)
-			return page;
+			break;
 	}
 
-	return ERR_PTR(-ENOMEM);
+	return page;
 }
 
 /**
@@ -592,6 +602,7 @@ struct sgx_epc_page *sgx_alloc_epc_page(void *owner, bool reclaim)
 void sgx_free_epc_page(struct sgx_epc_page *page)
 {
 	struct sgx_epc_section *section = &sgx_epc_sections[page->section];
+	struct sgx_numa_node *node = section->node;
 	int ret;
 
 	WARN_ON_ONCE(page->flags & SGX_EPC_PAGE_RECLAIMER_TRACKED);
@@ -600,10 +611,12 @@ void sgx_free_epc_page(struct sgx_epc_page *page)
 	if (WARN_ONCE(ret, "EREMOVE returned %d (0x%x)", ret, ret))
 		return;
 
-	spin_lock(&section->lock);
-	list_add_tail(&page->list, &section->page_list);
-	section->free_cnt++;
-	spin_unlock(&section->lock);
+	spin_lock(&node->lock);
+
+	list_add_tail(&page->list, &node->free_page_list);
+	sgx_nr_free_pages++;
+
+	spin_unlock(&node->lock);
 }
 
 static bool __init sgx_setup_epc_section(u64 phys_addr, u64 size,
@@ -624,8 +637,6 @@ static bool __init sgx_setup_epc_section(u64 phys_addr, u64 size,
 	}
 
 	section->phys_addr = phys_addr;
-	spin_lock_init(&section->lock);
-	INIT_LIST_HEAD(&section->page_list);
 
 	for (i = 0; i < nr_pages; i++) {
 		section->pages[i].section = index;
@@ -634,7 +645,7 @@ static bool __init sgx_setup_epc_section(u64 phys_addr, u64 size,
 		list_add_tail(&section->pages[i].list, &sgx_dirty_page_list);
 	}
 
-	section->free_cnt = nr_pages;
+	sgx_nr_free_pages += nr_pages;
 	return true;
 }
 
@@ -653,8 +664,11 @@ static bool __init sgx_page_cache_init(void)
 {
 	u32 eax, ebx, ecx, edx, type;
 	u64 pa, size;
+	int nid;
 	int i;
 
+	sgx_numa_nodes = kmalloc_array(num_possible_nodes(), sizeof(*sgx_numa_nodes), GFP_KERNEL);
+
 	for (i = 0; i < ARRAY_SIZE(sgx_epc_sections); i++) {
 		cpuid_count(SGX_CPUID, i + SGX_CPUID_EPC, &eax, &ebx, &ecx, &edx);
 
@@ -677,6 +691,21 @@ static bool __init sgx_page_cache_init(void)
 			break;
 		}
 
+		nid = numa_map_to_online_node(phys_to_target_node(pa));
+		if (nid == NUMA_NO_NODE) {
+			/* The physical address is already printed above. */
+			pr_warn(FW_BUG "Unable to map EPC section to online node. Fallback to the NUMA node 0.\n");
+			nid = 0;
+		}
+
+		if (!node_isset(nid, sgx_numa_mask)) {
+			spin_lock_init(&sgx_numa_nodes[nid].lock);
+			INIT_LIST_HEAD(&sgx_numa_nodes[nid].free_page_list);
+			node_set(nid, sgx_numa_mask);
+		}
+
+		sgx_epc_sections[i].node =  &sgx_numa_nodes[nid];
+
 		sgx_nr_epc_sections++;
 	}
 
diff --git a/arch/x86/kernel/cpu/sgx/sgx.h b/arch/x86/kernel/cpu/sgx/sgx.h
index bc8af0428640..653af8ca1a25 100644
--- a/arch/x86/kernel/cpu/sgx/sgx.h
+++ b/arch/x86/kernel/cpu/sgx/sgx.h
@@ -29,22 +29,26 @@ struct sgx_epc_page {
 	struct list_head list;
 };
 
+/*
+ * Contains the tracking data for NUMA nodes having EPC pages. Most importantly,
+ * the free page list local to the node is stored here.
+ */
+struct sgx_numa_node {
+	struct list_head free_page_list;
+	spinlock_t lock;
+};
+
 /*
  * The firmware can define multiple chunks of EPC to the different areas of the
  * physical memory e.g. for memory areas of the each node. This structure is
  * used to store EPC pages for one EPC section and virtual memory area where
  * the pages have been mapped.
- *
- * 'lock' must be held before accessing 'page_list' or 'free_cnt'.
  */
 struct sgx_epc_section {
 	unsigned long phys_addr;
 	void *virt_addr;
 	struct sgx_epc_page *pages;
-
-	spinlock_t lock;
-	struct list_head page_list;
-	unsigned long free_cnt;
+	struct sgx_numa_node *node;
 };
 
 extern struct sgx_epc_section sgx_epc_sections[SGX_MAX_EPC_SECTIONS];
-- 
2.30.2