linux-kernel - [PATCH v5 1/3] x86/sgx: Split SGX_ENCL_PAGE_BEING

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Message-Id: <20240821100215.4119457-2-dmitrii.kuvaiskii@intel.com>
Date: Wed, 21 Aug 2024 03:02:13 -0700
From: Dmitrii Kuvaiskii <dmitrii.kuvaiskii@...el.com>
To: dave.hansen@...ux.intel.com,
	jarkko@...nel.org,
	kai.huang@...el.com,
	haitao.huang@...ux.intel.com,
	reinette.chatre@...el.com,
	linux-sgx@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: mona.vij@...el.com,
	kailun.qin@...el.com,
	stable@...r.kernel.org
Subject: [PATCH v5 1/3] x86/sgx: Split SGX_ENCL_PAGE_BEING_RECLAIMED into two flags

The page reclaimer thread sets SGX_ENC_PAGE_BEING_RECLAIMED flag when
the enclave page is being reclaimed (moved to the backing store). This
flag however has two logical meanings:

1. Don't attempt to load the enclave page (the page is busy), see
   __sgx_encl_load_page().
2. Don't attempt to remove the PCMD page corresponding to this enclave
   page (the PCMD page is busy), see reclaimer_writing_to_pcmd().

To reflect these two meanings, split SGX_ENCL_PAGE_BEING_RECLAIMED into
two flags: SGX_ENCL_PAGE_BUSY and SGX_ENCL_PAGE_PCMD_BUSY. Currently,
both flags are set only when the enclave page is being reclaimed (by the
page reclaimer thread). A future commit will introduce new cases when
the enclave page is being operated on; these new cases will set only the
SGX_ENCL_PAGE_BUSY flag.

Cc: stable@...r.kernel.org
Signed-off-by: Dmitrii Kuvaiskii <dmitrii.kuvaiskii@...el.com>
Reviewed-by: Haitao Huang <haitao.huang@...ux.intel.com>
Acked-by: Kai Huang <kai.huang@...el.com>
---
 arch/x86/kernel/cpu/sgx/encl.c | 16 +++++++---------
 arch/x86/kernel/cpu/sgx/encl.h | 10 ++++++++--
 arch/x86/kernel/cpu/sgx/main.c |  4 ++--
 3 files changed, 17 insertions(+), 13 deletions(-)

diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c
index 279148e72459..c0a3c00284c8 100644
--- a/arch/x86/kernel/cpu/sgx/encl.c
+++ b/arch/x86/kernel/cpu/sgx/encl.c
@@ -46,10 +46,10 @@ static int sgx_encl_lookup_backing(struct sgx_encl *encl, unsigned long page_ind
  * a check if an enclave page sharing the PCMD page is in the process of being
  * reclaimed.
  *
- * The reclaimer sets the SGX_ENCL_PAGE_BEING_RECLAIMED flag when it
- * intends to reclaim that enclave page - it means that the PCMD page
- * associated with that enclave page is about to get some data and thus
- * even if the PCMD page is empty, it should not be truncated.
+ * The reclaimer sets the SGX_ENCL_PAGE_PCMD_BUSY flag when it intends to
+ * reclaim that enclave page - it means that the PCMD page associated with that
+ * enclave page is about to get some data and thus even if the PCMD page is
+ * empty, it should not be truncated.
  *
  * Context: Enclave mutex (&sgx_encl->lock) must be held.
  * Return: 1 if the reclaimer is about to write to the PCMD page
@@ -77,8 +77,7 @@ static int reclaimer_writing_to_pcmd(struct sgx_encl *encl,
 		 * Stop when reaching the SECS page - it does not
 		 * have a page_array entry and its reclaim is
 		 * started and completed with enclave mutex held so
-		 * it does not use the SGX_ENCL_PAGE_BEING_RECLAIMED
-		 * flag.
+		 * it does not use the SGX_ENCL_PAGE_PCMD_BUSY flag.
 		 */
 		if (addr == encl->base + encl->size)
 			break;
@@ -91,8 +90,7 @@ static int reclaimer_writing_to_pcmd(struct sgx_encl *encl,
 		 * VA page slot ID uses same bit as the flag so it is important
 		 * to ensure that the page is not already in backing store.
 		 */
-		if (entry->epc_page &&
-		    (entry->desc & SGX_ENCL_PAGE_BEING_RECLAIMED)) {
+		if (entry->epc_page && (entry->desc & SGX_ENCL_PAGE_PCMD_BUSY)) {
 			reclaimed = 1;
 			break;
 		}
@@ -257,7 +255,7 @@ static struct sgx_encl_page *__sgx_encl_load_page(struct sgx_encl *encl,
 
 	/* Entry successfully located. */
 	if (entry->epc_page) {
-		if (entry->desc & SGX_ENCL_PAGE_BEING_RECLAIMED)
+		if (entry->desc & SGX_ENCL_PAGE_BUSY)
 			return ERR_PTR(-EBUSY);
 
 		return entry;
diff --git a/arch/x86/kernel/cpu/sgx/encl.h b/arch/x86/kernel/cpu/sgx/encl.h
index f94ff14c9486..b566b8ad5f33 100644
--- a/arch/x86/kernel/cpu/sgx/encl.h
+++ b/arch/x86/kernel/cpu/sgx/encl.h
@@ -22,8 +22,14 @@
 /* 'desc' bits holding the offset in the VA (version array) page. */
 #define SGX_ENCL_PAGE_VA_OFFSET_MASK	GENMASK_ULL(11, 3)
 
-/* 'desc' bit marking that the page is being reclaimed. */
-#define SGX_ENCL_PAGE_BEING_RECLAIMED	BIT(3)
+/* 'desc' bit indicating that the page is busy (being reclaimed). */
+#define SGX_ENCL_PAGE_BUSY	BIT(2)
+
+/*
+ * 'desc' bit indicating that PCMD page associated with the enclave page is
+ * busy (because the enclave page is being reclaimed).
+ */
+#define SGX_ENCL_PAGE_PCMD_BUSY	BIT(3)
 
 struct sgx_encl_page {
 	unsigned long desc;
diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
index 166692f2d501..e94b09c43673 100644
--- a/arch/x86/kernel/cpu/sgx/main.c
+++ b/arch/x86/kernel/cpu/sgx/main.c
@@ -204,7 +204,7 @@ static void sgx_encl_ewb(struct sgx_epc_page *epc_page,
 	void *va_slot;
 	int ret;
 
-	encl_page->desc &= ~SGX_ENCL_PAGE_BEING_RECLAIMED;
+	encl_page->desc &= ~(SGX_ENCL_PAGE_BUSY | SGX_ENCL_PAGE_PCMD_BUSY);
 
 	va_page = list_first_entry(&encl->va_pages, struct sgx_va_page,
 				   list);
@@ -340,7 +340,7 @@ static void sgx_reclaim_pages(void)
 			goto skip;
 		}
 
-		encl_page->desc |= SGX_ENCL_PAGE_BEING_RECLAIMED;
+		encl_page->desc |= SGX_ENCL_PAGE_BUSY | SGX_ENCL_PAGE_PCMD_BUSY;
 		mutex_unlock(&encl_page->encl->lock);
 		continue;
 
-- 
2.43.0