linux-kernel - [tip: x86/mm] mm: Update ptep_get

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Date:   Sat, 17 Dec 2022 18:55:34 -0000
From:   "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Matthew Wilcox <willy@...radead.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: x86/mm] mm: Update ptep_get_lockless()'s comment

The following commit has been merged into the x86/mm branch of tip:

Commit-ID:     93b3037a1482758349f3b0431406bcc457ca1cbc
Gitweb:        https://git.kernel.org/tip/93b3037a1482758349f3b0431406bcc457ca1cbc
Author:        Peter Zijlstra <peterz@...radead.org>
AuthorDate:    Thu, 26 Nov 2020 14:04:46 +01:00
Committer:     Dave Hansen <dave.hansen@...ux.intel.com>
CommitterDate: Thu, 15 Dec 2022 10:37:27 -08:00

mm: Update ptep_get_lockless()'s comment

Improve the comment.

Suggested-by: Matthew Wilcox <willy@...radead.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lkml.kernel.org/r/20221022114424.515572025%40infradead.org
---
 include/linux/pgtable.h | 15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index a108b60..c0b2900 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -300,15 +300,12 @@ static inline pte_t ptep_get(pte_t *ptep)
 
 #ifdef CONFIG_GUP_GET_PTE_LOW_HIGH
 /*
- * WARNING: only to be used in the get_user_pages_fast() implementation.
- *
- * With get_user_pages_fast(), we walk down the pagetables without taking any
- * locks.  For this we would like to load the pointers atomically, but sometimes
- * that is not possible (e.g. without expensive cmpxchg8b on x86_32 PAE).  What
- * we do have is the guarantee that a PTE will only either go from not present
- * to present, or present to not present or both -- it will not switch to a
- * completely different present page without a TLB flush in between; something
- * that we are blocking by holding interrupts off.
+ * For walking the pagetables without holding any locks.  Some architectures
+ * (eg x86-32 PAE) cannot load the entries atomically without using expensive
+ * instructions.  We are guaranteed that a PTE will only either go from not
+ * present to present, or present to not present -- it will not switch to a
+ * completely different present page without a TLB flush inbetween; which we
+ * are blocking by holding interrupts off.
  *
  * Setting ptes from not present to present goes:
  *