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mm: clarify lazy_mmu sleeping constraints

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The lazy MMU mode documentation makes clear that an implementation should
not assume that preemption is disabled or any lock is held upon entry to
the mode; however it says nothing about what code using the lazy MMU
interface should expect.

In practice sleeping is forbidden (for generic code) while the lazy MMU
mode is active: say it explicitly.

Link: https://lkml.kernel.org/r/20251215150323.2218608-6-kevin.brodsky@arm.com
Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>
Reviewed-by: Yeoreum Yun <yeoreum.yun@arm.com>
Acked-by: David Hildenbrand (Red Hat) <david@kernel.org>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Andreas Larsson <andreas@gaisler.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Borislav Betkov <bp@alien8.de>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: David S. Miller <davem@davemloft.net>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: Juegren Gross <jgross@suse.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Thomas Gleinxer <tglx@linutronix.de>
Cc: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Kevin Brodsky 2025-12-15 15:03:14 +00:00 • committed by Andrew Morton
parent 442bf488b9
commit f2be745071
1 changed files with 9 additions and 5 deletions
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14
include/linux/pgtable.h
View file

@ -225,11 +225,15 @@ static inline int pmd_dirty(pmd_t pmd)
* up to date.
*
* In the general case, no lock is guaranteed to be held between entry and exit
* of the lazy mode. So the implementation must assume preemption may be enabled
* and cpu migration is possible; it must take steps to be robust against this.
* (In practice, for user PTE updates, the appropriate page table lock(s) are
* held, but for kernel PTE updates, no lock is held). Nesting is not permitted
* and the mode cannot be used in interrupt context.
* of the lazy mode. (In practice, for user PTE updates, the appropriate page
* table lock(s) are held, but for kernel PTE updates, no lock is held).
* The implementation must therefore assume preemption may be enabled upon
* entry to the mode and cpu migration is possible; it must take steps to be
* robust against this. An implementation may handle this by disabling
* preemption, as a consequence generic code may not sleep while the lazy MMU
* mode is active.
*
* Nesting is not permitted and the mode cannot be used in interrupt context.
*/
#ifndef __HAVE_ARCH_ENTER_LAZY_MMU_MODE
static inline void arch_enter_lazy_mmu_mode(void) {}