linux-kernel - [PATCH v1] arm64: mm: Batch dsb and isb when populating pgtables

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Date: Wed, 27 Mar 2024 19:07:23 +0000
From: Ryan Roberts <ryan.roberts@....com>
To: Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Ard Biesheuvel <ardb@...nel.org>,
	David Hildenbrand <david@...hat.com>,
	Donald Dutile <ddutile@...hat.com>,
	Eric Chanudet <echanude@...hat.com>
Cc: Ryan Roberts <ryan.roberts@....com>,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH v1] arm64: mm: Batch dsb and isb when populating pgtables

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.

Signed-off-by: Ryan Roberts <ryan.roberts@....com>
---
 arch/arm64/include/asm/pgtable.h |  7 ++++++-
 arch/arm64/mm/mmu.c              | 13 ++++++++++++-
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index bd5d02f3f0a3..81e427b23b3f 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -271,9 +271,14 @@ static inline pte_t pte_mkdevmap(pte_t pte)
 	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(pte_t *ptep, pte_t pte)
 {
 	WRITE_ONCE(*ptep, pte);
+}
+
+static inline void __set_pte(pte_t *ptep, pte_t pte)
+{
+	___set_pte(ptep, pte);

 	/*
 	 * Only if the new pte is valid and kernel, otherwise TLB maintenance
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 1b2a2a2d09b7..c6d5a76732d4 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -301,7 +301,11 @@ static pte_t *init_pte(pte_t *ptep, unsigned long addr, unsigned long end,
 	do {
 		pte_t old_pte = __ptep_get(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(ptep, pfn_pte(__phys_to_pfn(phys), prot));

 		/*
 		 * After the PTE entry has been populated once, we
@@ -358,6 +362,13 @@ static void alloc_init_cont_pte(pmd_t *pmdp, unsigned long addr,
 	} while (addr = next, addr != end);

 	ops->unmap(TYPE_PTE);
+
+	/*
+	 * Ensure all previous pgtable writes are visible to the table walker.
+	 * See init_pte().
+	 */
+	dsb(ishst);
+	isb();
 }

 static pmd_t *init_pmd(pmd_t *pmdp, unsigned long addr, unsigned long end,
--
2.25.1