[PATCH v6 07/12] x86/sgx: Introduce EPC page states

Haitao Huang
2023-10-30T18:21:08Z

Use the lower 2 bits in the flags field of sgx_epc_page struct to track
EPC states and define an enum for possible states for EPC pages tracked
for reclamation.

Add the RECLAIM_IN_PROGRESS state to explicitly indicate a page that is
identified as a candidate for reclaiming, but has not yet been
reclaimed, instead of relying on list_empty(&epc_page->list). A later
patch will replace the array on stack with a temporary list to store the
candidate pages, so list_empty() should no longer be used for this
purpose.

Co-developed-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Co-developed-by: Kristen Carlson Accardi <kristen@linux.intel.com>
Signed-off-by: Kristen Carlson Accardi <kristen@linux.intel.com>
Signed-off-by: Haitao Huang <haitao.huang@linux.intel.com>
Cc: Sean Christopherson <seanjc@google.com>
---
V6:
- Drop UNRECLAIMABLE and use only 2 bits for states (Kai)
- Combine the patch for RECLAIM_IN_PROGRESS
- Style fixes (Jarkko and Kai)
---
arch/x86/kernel/cpu/sgx/encl.c | 2 +-
arch/x86/kernel/cpu/sgx/main.c | 33 +++++++++---------
arch/x86/kernel/cpu/sgx/sgx.h | 62 +++++++++++++++++++++++++++++++---
3 files changed, 76 insertions(+), 21 deletions(-)

diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c
index 279148e72459..17dc108d3ff7 100644
--- a/arch/x86/kernel/cpu/sgx/encl.c
+++ b/arch/x86/kernel/cpu/sgx/encl.c
@@ -1315,7 +1315,7 @@ void sgx_encl_free_epc_page(struct sgx_epc_page *page)
{
int ret;

- WARN_ON_ONCE(page->flags & SGX_EPC_PAGE_RECLAIMER_TRACKED);
+ WARN_ON_ONCE(page->flags & SGX_EPC_PAGE_STATE_MASK);

ret = __eremove(sgx_get_epc_virt_addr(page));
if (WARN_ONCE(ret, EREMOVE_ERROR_MESSAGE, ret, ret))
diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
index d347acd717fd..e27ac73d8843 100644
--- a/arch/x86/kernel/cpu/sgx/main.c
+++ b/arch/x86/kernel/cpu/sgx/main.c
@@ -315,13 +315,14 @@ static void sgx_reclaim_pages(void)
list_del_init(&epc_page->list);
encl_page = epc_page->owner;

- if (kref_get_unless_zero(&encl_page->encl->refcount) != 0)
+ if (kref_get_unless_zero(&encl_page->encl->refcount) != 0) {
+ sgx_epc_page_set_state(epc_page, SGX_EPC_PAGE_RECLAIM_IN_PROGRESS);
chunk[cnt++] = epc_page;
- else
+ } else
/* The owner is freeing the page. No need to add the
* page back to the list of reclaimable pages.
*/
- epc_page->flags &= ~SGX_EPC_PAGE_RECLAIMER_TRACKED;
+ sgx_epc_page_reset_state(epc_page);
}
spin_unlock(&sgx_global_lru.lock);

@@ -347,6 +348,7 @@ static void sgx_reclaim_pages(void)

skip:
spin_lock(&sgx_global_lru.lock);
+ sgx_epc_page_set_state(epc_page, SGX_EPC_PAGE_RECLAIMABLE);
list_add_tail(&epc_page->list, &sgx_global_lru.reclaimable);
spin_unlock(&sgx_global_lru.lock);

@@ -370,7 +372,7 @@ static void sgx_reclaim_pages(void)
sgx_reclaimer_write(epc_page, &backing[i]);

kref_put(&encl_page->encl->refcount, sgx_encl_release);
- epc_page->flags &= ~SGX_EPC_PAGE_RECLAIMER_TRACKED;
+ sgx_epc_page_reset_state(epc_page);

sgx_free_epc_page(epc_page);
}
@@ -509,7 +511,8 @@ struct sgx_epc_page *__sgx_alloc_epc_page(void)
void sgx_mark_page_reclaimable(struct sgx_epc_page *page)
{
spin_lock(&sgx_global_lru.lock);
- page->flags |= SGX_EPC_PAGE_RECLAIMER_TRACKED;
+ WARN_ON_ONCE(sgx_epc_page_reclaimable(page->flags));
+ page->flags |= SGX_EPC_PAGE_RECLAIMABLE;
list_add_tail(&page->list, &sgx_global_lru.reclaimable);
spin_unlock(&sgx_global_lru.lock);
}
@@ -527,16 +530,13 @@ void sgx_mark_page_reclaimable(struct sgx_epc_page *page)
int sgx_unmark_page_reclaimable(struct sgx_epc_page *page)
{
spin_lock(&sgx_global_lru.lock);
- if (page->flags & SGX_EPC_PAGE_RECLAIMER_TRACKED) {
- /* The page is being reclaimed. */
- if (list_empty(&page->list)) {
- spin_unlock(&sgx_global_lru.lock);
- return -EBUSY;
- }
-
- list_del(&page->list);
- page->flags &= ~SGX_EPC_PAGE_RECLAIMER_TRACKED;
+ if (sgx_epc_page_reclaim_in_progress(page->flags)) {
+ spin_unlock(&sgx_global_lru.lock);
+ return -EBUSY;
}
+
+ list_del(&page->list);
+ sgx_epc_page_reset_state(page);
spin_unlock(&sgx_global_lru.lock);

return 0;
@@ -623,6 +623,7 @@ 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;

+ WARN_ON_ONCE(page->flags & (SGX_EPC_PAGE_STATE_MASK));
if (page->epc_cg) {
sgx_epc_cgroup_uncharge(page->epc_cg);
page->epc_cg = NULL;
@@ -635,7 +636,7 @@ void sgx_free_epc_page(struct sgx_epc_page *page)
list_add(&page->list, &node->sgx_poison_page_list);
else
list_add_tail(&page->list, &node->free_page_list);
- page->flags = SGX_EPC_PAGE_IS_FREE;
+ page->flags = SGX_EPC_PAGE_FREE;

spin_unlock(&node->lock);
atomic_long_inc(&sgx_nr_free_pages);
@@ -737,7 +738,7 @@ int arch_memory_failure(unsigned long pfn, int flags)
* If the page is on a free list, move it to the per-node
* poison page list.
*/
- if (page->flags & SGX_EPC_PAGE_IS_FREE) {
+ if (page->flags == SGX_EPC_PAGE_FREE) {
list_move(&page->list, &node->sgx_poison_page_list);
goto out;
}
diff --git a/arch/x86/kernel/cpu/sgx/sgx.h b/arch/x86/kernel/cpu/sgx/sgx.h
index 0fbe6a2a159b..dd7ab65b5b27 100644
--- a/arch/x86/kernel/cpu/sgx/sgx.h
+++ b/arch/x86/kernel/cpu/sgx/sgx.h
@@ -23,11 +23,44 @@
#define SGX_NR_LOW_PAGES 32
#define SGX_NR_HIGH_PAGES 64

-/* Pages, which are being tracked by the page reclaimer. */
-#define SGX_EPC_PAGE_RECLAIMER_TRACKED BIT(0)
+enum sgx_epc_page_state {
+ /*
+ * Allocated but not tracked by the reclaimer.
+ *
+ * Pages allocated for virtual EPC which are never tracked by the host
+ * reclaimer; pages just allocated from free list but not yet put in
+ * use; pages just reclaimed, but not yet returned to the free list.
+ * Becomes FREE after sgx_free_epc().
+ * Becomes RECLAIMABLE after sgx_mark_page_reclaimable().
+ */
+ SGX_EPC_PAGE_NOT_TRACKED = 0,
+
+ /*
+ * Page is in the free list, ready for allocation.
+ *
+ * Becomes NOT_TRACKED after sgx_alloc_epc_page().
+ */
+ SGX_EPC_PAGE_FREE = 1,
+
+ /*
+ * Page is in use and tracked in a reclaimable LRU list.
+ *
+ * Becomes NOT_TRACKED after sgx_unmark_page_reclaimable().
+ * Becomes RECLAIM_IN_PROGRESS in sgx_reclaim_pages() when identified
+ * for reclaiming.
+ */
+ SGX_EPC_PAGE_RECLAIMABLE = 2,
+
+ /*
+ * Page is in the middle of reclamation.
+ *
+ * Back to RECLAIMABLE if reclamation fails for any reason.
+ * Becomes NOT_TRACKED if reclaimed successfully.
+ */
+ SGX_EPC_PAGE_RECLAIM_IN_PROGRESS = 3,
+};

-/* Pages on free list */
-#define SGX_EPC_PAGE_IS_FREE BIT(1)
+#define SGX_EPC_PAGE_STATE_MASK GENMASK(1, 0)

struct sgx_epc_cgroup;

@@ -40,6 +73,27 @@ struct sgx_epc_page {
struct sgx_epc_cgroup *epc_cg;
};

+static inline void sgx_epc_page_reset_state(struct sgx_epc_page *page)
+{
+ page->flags &= ~SGX_EPC_PAGE_STATE_MASK;
+}
+
+static inline void sgx_epc_page_set_state(struct sgx_epc_page *page, unsigned long flags)
+{
+ page->flags &= ~SGX_EPC_PAGE_STATE_MASK;
+ page->flags |= (flags & SGX_EPC_PAGE_STATE_MASK);
+}
+
+static inline bool sgx_epc_page_reclaim_in_progress(unsigned long flags)
+{
+ return SGX_EPC_PAGE_RECLAIM_IN_PROGRESS == (flags & SGX_EPC_PAGE_STATE_MASK);
+}
+
+static inline bool sgx_epc_page_reclaimable(unsigned long flags)
+{
+ return SGX_EPC_PAGE_RECLAIMABLE == (flags & SGX_EPC_PAGE_STATE_MASK);
+}
+
/*
* Contains the tracking data for NUMA nodes having EPC pages. Most importantly,
* the free page list local to the node is stored here.
--
2.25.1