linux-kernel - [PATCH 7/7] mm: update lazy

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Message-ID: <20250904125736.3918646-8-kevin.brodsky@arm.com>
Date: Thu,  4 Sep 2025 13:57:36 +0100
From: Kevin Brodsky <kevin.brodsky@....com>
To: linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org,
	Kevin Brodsky <kevin.brodsky@....com>,
	Alexander Gordeev <agordeev@...ux.ibm.com>,
	Andreas Larsson <andreas@...sler.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Borislav Petkov <bp@...en8.de>,
	Catalin Marinas <catalin.marinas@....com>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	David Hildenbrand <david@...hat.com>,
	"David S. Miller" <davem@...emloft.net>,
	"H. Peter Anvin" <hpa@...or.com>,
	Ingo Molnar <mingo@...hat.com>,
	Jann Horn <jannh@...gle.com>,
	Juergen Gross <jgross@...e.com>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Madhavan Srinivasan <maddy@...ux.ibm.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Michal Hocko <mhocko@...e.com>,
	Mike Rapoport <rppt@...nel.org>,
	Nicholas Piggin <npiggin@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ryan Roberts <ryan.roberts@....com>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Vlastimil Babka <vbabka@...e.cz>,
	Will Deacon <will@...nel.org>,
	linux-arm-kernel@...ts.infradead.org,
	linuxppc-dev@...ts.ozlabs.org,
	sparclinux@...r.kernel.org,
	xen-devel@...ts.xenproject.org
Subject: [PATCH 7/7] mm: update lazy_mmu documentation

We now support nested lazy_mmu sections on all architectures
implementing the API. Update the API comment accordingly.

Signed-off-by: Kevin Brodsky <kevin.brodsky@....com>
---
 include/linux/pgtable.h | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index 6932c8e344ab..be0f059beb4d 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -228,8 +228,18 @@ static inline int pmd_dirty(pmd_t pmd)
  * 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.
+ * held, but for kernel PTE updates, no lock is held). The mode cannot be used
+ * in interrupt context.
+ *
+ * Calls may be nested: an arch_{enter,leave}_lazy_mmu_mode() pair may be called
+ * while the lazy MMU mode has already been enabled. An implementation should
+ * handle this using the state returned by enter() and taken by the matching
+ * leave() call; the LAZY_MMU_{DEFAULT,NESTED} flags can be used to indicate
+ * whether this enter/leave pair is nested inside another or not. (It is up to
+ * the implementation to track whether the lazy MMU mode is enabled at any point
+ * in time.) The expectation is that leave() will flush any batched state
+ * unconditionally, but only leave the lazy MMU mode if the passed state is not
+ * LAZY_MMU_NESTED.
  */
 #ifndef __HAVE_ARCH_ENTER_LAZY_MMU_MODE
 typedef int lazy_mmu_state_t;
-- 
2.47.0