linux-kernel - [PATCH v2 06/18] x86/sgx: Introduce RECLAIM_IN

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Date:   Fri,  2 Dec 2022 10:36:42 -0800
From:   Kristen Carlson Accardi <kristen@...ux.intel.com>
To:     jarkko@...nel.org, dave.hansen@...ux.intel.com, tj@...nel.org,
        linux-kernel@...r.kernel.org, linux-sgx@...r.kernel.org,
        cgroups@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>
Cc:     zhiquan1.li@...el.com,
        Kristen Carlson Accardi <kristen@...ux.intel.com>,
        Sean Christopherson <seanjc@...gle.com>
Subject: [PATCH v2 06/18] x86/sgx: Introduce RECLAIM_IN_PROGRESS flag for EPC pages

From: Sean Christopherson <sean.j.christopherson@...el.com>

When selecting pages to be reclaimed from the page pool (sgx_global_lru),
the list of reclaimable pages is walked, and any page that is both
reclaimable and not in the process of being freed is added to a list of
potential candidates to be reclaimed. After that, this separate list is
further examined and may or may not ultimately be reclaimed. In order
to prevent this page from being removed from the sgx_epc_lru_lists
struct in a separate thread by sgx_drop_epc_page(), keep track of
whether the EPC page is in the middle of being reclaimed with
the addtion of a RECLAIM_IN_PROGRESS flag, and do not delete the page
off the LRU in sgx_drop_epc_page() if it has not yet finished being
reclaimed.

Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
Signed-off-by: Kristen Carlson Accardi <kristen@...ux.intel.com>
Cc: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kernel/cpu/sgx/main.c | 15 ++++++++++-----
 arch/x86/kernel/cpu/sgx/sgx.h  |  2 ++
 2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
index ecd7f8e704cc..bad72498b0a7 100644
--- a/arch/x86/kernel/cpu/sgx/main.c
+++ b/arch/x86/kernel/cpu/sgx/main.c
@@ -305,13 +305,15 @@ static void __sgx_reclaim_pages(void)
 
 		encl_page = epc_page->encl_owner;
 
-		if (kref_get_unless_zero(&encl_page->encl->refcount) != 0)
+		if (kref_get_unless_zero(&encl_page->encl->refcount) != 0) {
+			epc_page->flags |= 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;
+		}
 	}
 	spin_unlock(&sgx_global_lru.lock);
 
@@ -337,6 +339,7 @@ static void __sgx_reclaim_pages(void)
 
 skip:
 		spin_lock(&sgx_global_lru.lock);
+		epc_page->flags &= ~SGX_EPC_PAGE_RECLAIM_IN_PROGRESS;
 		sgx_epc_push_reclaimable(&sgx_global_lru, epc_page);
 		spin_unlock(&sgx_global_lru.lock);
 
@@ -360,7 +363,8 @@ 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;
+		epc_page->flags &= ~(SGX_EPC_PAGE_RECLAIMER_TRACKED |
+				     SGX_EPC_PAGE_RECLAIM_IN_PROGRESS);
 
 		sgx_free_epc_page(epc_page);
 	}
@@ -508,7 +512,8 @@ struct sgx_epc_page *__sgx_alloc_epc_page(void)
 void sgx_record_epc_page(struct sgx_epc_page *page, unsigned long flags)
 {
 	spin_lock(&sgx_global_lru.lock);
-	WARN_ON(page->flags & SGX_EPC_PAGE_RECLAIMER_TRACKED);
+	WARN_ON(page->flags & (SGX_EPC_PAGE_RECLAIMER_TRACKED |
+			       SGX_EPC_PAGE_RECLAIM_IN_PROGRESS));
 	page->flags |= flags;
 	if (flags & SGX_EPC_PAGE_RECLAIMER_TRACKED)
 		sgx_epc_push_reclaimable(&sgx_global_lru, page);
@@ -532,7 +537,7 @@ int sgx_drop_epc_page(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)) {
+		if (page->flags & SGX_EPC_PAGE_RECLAIM_IN_PROGRESS) {
 			spin_unlock(&sgx_global_lru.lock);
 			return -EBUSY;
 		}
diff --git a/arch/x86/kernel/cpu/sgx/sgx.h b/arch/x86/kernel/cpu/sgx/sgx.h
index ba4338b7303f..37d66bc6ca27 100644
--- a/arch/x86/kernel/cpu/sgx/sgx.h
+++ b/arch/x86/kernel/cpu/sgx/sgx.h
@@ -30,6 +30,8 @@
 #define SGX_EPC_PAGE_IS_FREE		BIT(1)
 /* Pages allocated for KVM guest */
 #define SGX_EPC_PAGE_KVM_GUEST		BIT(2)
+/* page flag to indicate reclaim is in progress */
+#define SGX_EPC_PAGE_RECLAIM_IN_PROGRESS BIT(3)
 
 struct sgx_epc_page {
 	unsigned int section;
-- 
2.38.1