Commit 93b3037a authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Dave Hansen
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mm: Update ptep_get_lockless()'s comment 



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Suggested-by: default avatarMatthew Wilcox <willy@infradead.org>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20221022114424.515572025%40infradead.org
parent 60463628

include/linux/pgtable.h

+6 −9
Original line number Diff line number Diff line
@@ -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:

 *