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mm: clarify lazy_mmu sleeping constraints

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>

authored by

Kevin Brodsky and committed by
Andrew Morton f2be7450 442bf488

+9 -5
+9 -5
include/linux/pgtable.h
··· 225 225 * up to date. 226 226 * 227 227 * In the general case, no lock is guaranteed to be held between entry and exit 228 - * of the lazy mode. So the implementation must assume preemption may be enabled 229 - * and cpu migration is possible; it must take steps to be robust against this. 230 - * (In practice, for user PTE updates, the appropriate page table lock(s) are 231 - * held, but for kernel PTE updates, no lock is held). Nesting is not permitted 232 - * and the mode cannot be used in interrupt context. 228 + * of the lazy mode. (In practice, for user PTE updates, the appropriate page 229 + * table lock(s) are held, but for kernel PTE updates, no lock is held). 230 + * The implementation must therefore assume preemption may be enabled upon 231 + * entry to the mode and cpu migration is possible; it must take steps to be 232 + * robust against this. An implementation may handle this by disabling 233 + * preemption, as a consequence generic code may not sleep while the lazy MMU 234 + * mode is active. 235 + * 236 + * Nesting is not permitted and the mode cannot be used in interrupt context. 233 237 */ 234 238 #ifndef __HAVE_ARCH_ENTER_LAZY_MMU_MODE 235 239 static inline void arch_enter_lazy_mmu_mode(void) {}