[PATCH v7 1/7] x86/sgx: Add new sgx_epc_page flag bit to mark in-use pages

[Tony Luck <tony.luck@xxxxxxxxx>]

SGX EPC pages go through the following life cycle:

        DIRTY ---> FREE ---> IN-USE --\
                    ^                 |
                    \-----------------/

Recovery action for poison for a DIRTY or FREE page is simple. Just
make sure never to allocate the page. IN-USE pages need some extra
handling.

Add a new flag bit SGX_EPC_PAGE_IN_USE that is set when a page
is allocated and cleared when the page is freed.

Notes:

1) These transitions are made while holding the node->lock so that
   future code that checks the flags while holding the node->lock
   can be sure that if the SGX_EPC_PAGE_IN_USE bit is set, then the
   page is on the free list.

2) Initially while the pages are on the dirty list the
   SGX_EPC_PAGE_IN_USE bit is set.

Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx>
---
 arch/x86/kernel/cpu/sgx/main.c | 4 +++-
 arch/x86/kernel/cpu/sgx/sgx.h  | 3 +++
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
index 63d3de02bbcc..d18988a46c13 100644
--- a/arch/x86/kernel/cpu/sgx/main.c
+++ b/arch/x86/kernel/cpu/sgx/main.c
@@ -472,6 +472,7 @@ static struct sgx_epc_page *__sgx_alloc_epc_page_from_node(int nid)
 	page = list_first_entry(&node->free_page_list, struct sgx_epc_page, list);
 	list_del_init(&page->list);
 	sgx_nr_free_pages--;
+	page->flags = SGX_EPC_PAGE_IN_USE;
 
 	spin_unlock(&node->lock);
 
@@ -626,6 +627,7 @@ void sgx_free_epc_page(struct sgx_epc_page *page)
 
 	list_add_tail(&page->list, &node->free_page_list);
 	sgx_nr_free_pages++;
+	page->flags = 0;
 
 	spin_unlock(&node->lock);
 }
@@ -651,7 +653,7 @@ 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].flags = SGX_EPC_PAGE_IN_USE;
 		section->pages[i].owner = NULL;
 		list_add_tail(&section->pages[i].list, &sgx_dirty_page_list);
 	}
diff --git a/arch/x86/kernel/cpu/sgx/sgx.h b/arch/x86/kernel/cpu/sgx/sgx.h
index 4628acec0009..f9202d3d6278 100644
--- a/arch/x86/kernel/cpu/sgx/sgx.h
+++ b/arch/x86/kernel/cpu/sgx/sgx.h
@@ -26,6 +26,9 @@
 /* Pages, which are being tracked by the page reclaimer. */
 #define SGX_EPC_PAGE_RECLAIMER_TRACKED	BIT(0)
 
+/* Allocated pages */
+#define SGX_EPC_PAGE_IN_USE		BIT(1)
+
 struct sgx_epc_page {
 	unsigned int section;
 	unsigned int flags;
-- 
2.31.1