[PATCH v6 3/7] x86/sgx: Initial poison handling for dirty and free pages

[Tony Luck <tony.luck@xxxxxxxxx>]

A memory controller patrol scrubber can report poison in a page
that isn't currently being used.

Add "poison" field in the sgx_epc_page that can be set for an
sgx_epc_page. Check for it:
1) When sanitizing dirty pages
2) When freeing epc pages

Poison is a new field separated from flags to avoid having to make
all updates to flags atomic, or integrate poison state changes into
some other locking scheme to protect flags.

In both cases place the poisoned page on a list of poisoned epc pages
to make sure it will not be reallocated.

Add debugfs files /sys/kernel/debug/sgx/poison_page_list so that system
administrators get a list of those pages that have been dropped because
of poison.

Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx>
---
 arch/x86/kernel/cpu/sgx/main.c | 30 +++++++++++++++++++++++++++++-
 arch/x86/kernel/cpu/sgx/sgx.h  |  3 ++-
 2 files changed, 31 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
index 72a173b3affa..91be079788ee 100644
--- a/arch/x86/kernel/cpu/sgx/main.c
+++ b/arch/x86/kernel/cpu/sgx/main.c
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 /*  Copyright(c) 2016-20 Intel Corporation. */
 
+#include <linux/debugfs.h>
 #include <linux/file.h>
 #include <linux/freezer.h>
 #include <linux/highmem.h>
@@ -43,6 +44,7 @@ static nodemask_t sgx_numa_mask;
 static struct sgx_numa_node *sgx_numa_nodes;
 
 static LIST_HEAD(sgx_dirty_page_list);
+static LIST_HEAD(sgx_poison_page_list);
 
 /*
  * Reset post-kexec EPC pages to the uninitialized state. The pages are removed
@@ -62,6 +64,12 @@ static void __sgx_sanitize_pages(struct list_head *dirty_page_list)
 
 		page = list_first_entry(dirty_page_list, struct sgx_epc_page, list);
 
+		if (page->poison) {
+			list_del(&page->list);
+			list_add(&page->list, &sgx_poison_page_list);
+			continue;
+		}
+
 		ret = __eremove(sgx_get_epc_virt_addr(page));
 		if (!ret) {
 			/*
@@ -626,7 +634,10 @@ void sgx_free_epc_page(struct sgx_epc_page *page)
 	spin_lock(&node->lock);
 
 	page->owner = NULL;
-	list_add_tail(&page->list, &node->free_page_list);
+	if (page->poison)
+		list_add(&page->list, &sgx_poison_page_list);
+	else
+		list_add_tail(&page->list, &node->free_page_list);
 	sgx_nr_free_pages++;
 
 	spin_unlock(&node->lock);
@@ -656,6 +667,7 @@ static bool __init sgx_setup_epc_section(u64 phys_addr, u64 size,
 	for (i = 0; i < nr_pages; i++) {
 		section->pages[i].section = index;
 		section->pages[i].flags = 0;
+		section->pages[i].poison = 0;
 		section->pages[i].owner = (void *)-1;
 		list_add_tail(&section->pages[i].list, &sgx_dirty_page_list);
 	}
@@ -800,8 +812,21 @@ int sgx_set_attribute(unsigned long *allowed_attributes,
 }
 EXPORT_SYMBOL_GPL(sgx_set_attribute);
 
+static int poison_list_show(struct seq_file *m, void *private)
+{
+	struct sgx_epc_page *page;
+
+	list_for_each_entry(page, &sgx_poison_page_list, list)
+		seq_printf(m, "0x%lx\n", sgx_get_epc_phys_addr(page));
+
+	return 0;
+}
+
+DEFINE_SHOW_ATTRIBUTE(poison_list);
+
 static int __init sgx_init(void)
 {
+	struct dentry *dir;
 	int ret;
 	int i;
 
@@ -833,6 +858,9 @@ static int __init sgx_init(void)
 	if (sgx_vepc_init() && ret)
 		goto err_provision;
 
+	dir = debugfs_create_dir("sgx", arch_debugfs_dir);
+	debugfs_create_file("poison_page_list", 0400, dir, NULL, &poison_list_fops);
+
 	return 0;
 
 err_provision:
diff --git a/arch/x86/kernel/cpu/sgx/sgx.h b/arch/x86/kernel/cpu/sgx/sgx.h
index cc624778645f..9ba87bc3da61 100644
--- a/arch/x86/kernel/cpu/sgx/sgx.h
+++ b/arch/x86/kernel/cpu/sgx/sgx.h
@@ -28,7 +28,8 @@
 
 struct sgx_epc_page {
 	unsigned int section;
-	unsigned int flags;
+	u16 flags;
+	u16 poison;
 	void *owner;
 	struct list_head list;
 };
-- 
2.31.1