Patch "arm64: mm: Batch dsb and isb when populating pgtables" has been added to the 6.6-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    arm64: mm: Batch dsb and isb when populating pgtables

to the 6.6-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     arm64-mm-batch-dsb-and-isb-when-populating-pgtables.patch
and it can be found in the queue-6.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


From stable+bounces-216826-greg=kroah.com@vger.kernel.org Tue Feb 17 14:35:05 2026
From: Ryan Roberts <ryan.roberts@arm.com>
Date: Tue, 17 Feb 2026 13:34:07 +0000
Subject: arm64: mm: Batch dsb and isb when populating pgtables
To: stable@vger.kernel.org
Cc: Ryan Roberts <ryan.roberts@arm.com>, catalin.marinas@arm.com, will@kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Jack Aboutboul <jaboutboul@microsoft.com>, Sharath George John <sgeorgejohn@microsoft.com>, Noah Meyerhans <nmeyerhans@microsoft.com>, Jim Perrin <Jim.Perrin@microsoft.com>, Itaru Kitayama <itaru.kitayama@fujitsu.com>, Eric Chanudet <echanude@redhat.com>, Mark Rutland <mark.rutland@arm.com>, Ard Biesheuvel <ardb@kernel.org>
Message-ID: <20260217133411.2881311-3-ryan.roberts@arm.com>

From: Ryan Roberts <ryan.roberts@arm.com>

[ Upstream commit 1fcb7cea8a5f7747e02230f816c2c80b060d9517 ]

After removing uneccessary TLBIs, the next bottleneck when creating the
page tables for the linear map is DSB and ISB, which were previously
issued per-pte in __set_pte(). Since we are writing multiple ptes in a
given pte table, we can elide these barriers and insert them once we
have finished writing to the table.

Execution time of map_mem(), which creates the kernel linear map page
tables, was measured on different machines with different RAM configs:

               | Apple M2 VM | Ampere Altra| Ampere Altra| Ampere Altra
               | VM, 16G     | VM, 64G     | VM, 256G    | Metal, 512G
---------------|-------------|-------------|-------------|-------------
               |   ms    (%) |   ms    (%) |   ms    (%) |    ms    (%)
---------------|-------------|-------------|-------------|-------------
before         |   78   (0%) |  435   (0%) | 1723   (0%) |  3779   (0%)
after          |   11 (-86%) |  161 (-63%) |  656 (-62%) |  1654 (-56%)

Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
Tested-by: Itaru Kitayama <itaru.kitayama@fujitsu.com>
Tested-by: Eric Chanudet <echanude@redhat.com>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20240412131908.433043-3-ryan.roberts@arm.com
Signed-off-by: Will Deacon <will@kernel.org>
[ Ryan: Trivial backport ]
Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/arm64/include/asm/pgtable.h |    7 ++++++-
 arch/arm64/mm/mmu.c              |   11 ++++++++++-
 2 files changed, 16 insertions(+), 2 deletions(-)

--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -262,9 +262,14 @@ static inline pte_t pte_mkdevmap(pte_t p
 	return set_pte_bit(pte, __pgprot(PTE_DEVMAP | PTE_SPECIAL));
 }
 
-static inline void set_pte(pte_t *ptep, pte_t pte)
+static inline void set_pte_nosync(pte_t *ptep, pte_t pte)
 {
 	WRITE_ONCE(*ptep, pte);
+}
+
+static inline void set_pte(pte_t *ptep, pte_t pte)
+{
+	set_pte_nosync(ptep, pte);
 
 	/*
 	 * Only if the new pte is valid and kernel, otherwise TLB maintenance
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -175,7 +175,11 @@ static void init_pte(pte_t *ptep, unsign
 	do {
 		pte_t old_pte = READ_ONCE(*ptep);
 
-		set_pte(ptep, pfn_pte(__phys_to_pfn(phys), prot));
+		/*
+		 * Required barriers to make this visible to the table walker
+		 * are deferred to the end of alloc_init_cont_pte().
+		 */
+		set_pte_nosync(ptep, pfn_pte(__phys_to_pfn(phys), prot));
 
 		/*
 		 * After the PTE entry has been populated once, we
@@ -229,6 +233,11 @@ static void alloc_init_cont_pte(pmd_t *p
 		phys += next - addr;
 	} while (addr = next, addr != end);
 
+	/*
+	 * Note: barriers and maintenance necessary to clear the fixmap slot
+	 * ensure that all previous pgtable writes are visible to the table
+	 * walker.
+	 */
 	pte_clear_fixmap();
 }
 


Patches currently in stable-queue which might be from ryan.roberts@arm.com are

queue-6.6/arm64-mm-don-t-remap-pgtables-per-cont-pte-pmd-block.patch
queue-6.6/arm64-mm-don-t-remap-pgtables-for-allocate-vs-populate.patch
queue-6.6/arm64-mm-batch-dsb-and-isb-when-populating-pgtables.patch