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Message-Id: <20220128131006.67712-15-michel@lespinasse.org>
Date: Fri, 28 Jan 2022 05:09:45 -0800
From: Michel Lespinasse <michel@...pinasse.org>
To: Linux-MM <linux-mm@...ck.org>, linux-kernel@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>
Cc: kernel-team@...com, Laurent Dufour <ldufour@...ux.ibm.com>,
Jerome Glisse <jglisse@...gle.com>,
Peter Zijlstra <peterz@...radead.org>,
Michal Hocko <mhocko@...e.com>,
Vlastimil Babka <vbabka@...e.cz>,
Davidlohr Bueso <dave@...olabs.net>,
Matthew Wilcox <willy@...radead.org>,
Liam Howlett <liam.howlett@...cle.com>,
Rik van Riel <riel@...riel.com>,
Paul McKenney <paulmck@...nel.org>,
Song Liu <songliubraving@...com>,
Suren Baghdasaryan <surenb@...gle.com>,
Minchan Kim <minchan@...gle.com>,
Joel Fernandes <joelaf@...gle.com>,
David Rientjes <rientjes@...gle.com>,
Axel Rasmussen <axelrasmussen@...gle.com>,
Andy Lutomirski <luto@...nel.org>,
Michel Lespinasse <michel@...pinasse.org>
Subject: [PATCH v2 14/35] mm: add speculative_page_walk_begin() and speculative_page_walk_end()
Speculative page faults will use these to protect against races with
page table reclamation.
This could always be handled by disabling local IRQs as the fast GUP
code does; however speculative page faults do not need to protect
against races with THP page splitting, so a weaker rcu read lock is
sufficient in the MMU_GATHER_RCU_TABLE_FREE case.
Signed-off-by: Michel Lespinasse <michel@...pinasse.org>
---
mm/memory.c | 22 ++++++++++++++++++++++
1 file changed, 22 insertions(+)
diff --git a/mm/memory.c b/mm/memory.c
index aa24cd8c06e9..663952d14bad 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2725,6 +2725,28 @@ int apply_to_existing_page_range(struct mm_struct *mm, unsigned long addr,
}
EXPORT_SYMBOL_GPL(apply_to_existing_page_range);
+#ifdef CONFIG_SPECULATIVE_PAGE_FAULT
+
+/*
+ * speculative_page_walk_begin() ... speculative_page_walk_end() protects
+ * against races with page table reclamation.
+ *
+ * This is similar to what fast GUP does, but fast GUP also needs to
+ * protect against races with THP page splitting, so it always needs
+ * to disable interrupts.
+ * Speculative page faults only need to protect against page table reclamation,
+ * so rcu_read_lock() is sufficient in the MMU_GATHER_RCU_TABLE_FREE case.
+ */
+#ifdef CONFIG_MMU_GATHER_RCU_TABLE_FREE
+#define speculative_page_walk_begin() rcu_read_lock()
+#define speculative_page_walk_end() rcu_read_unlock()
+#else
+#define speculative_page_walk_begin() local_irq_disable()
+#define speculative_page_walk_end() local_irq_enable()
+#endif
+
+#endif /* CONFIG_SPECULATIVE_PAGE_FAULT */
+
/*
* handle_pte_fault chooses page fault handler according to an entry which was
* read non-atomically. Before making any commitment, on those architectures
--
2.20.1
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