linux-kernel - [PATCH] riscv: Use an atomic xchg in pudp_huge_get_and

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Message-Id: <20250814-dev-alex-thp_pud_xchg-v1-1-b4704dfae206@rivosinc.com>
Date: Thu, 14 Aug 2025 12:06:14 +0000
From: Alexandre Ghiti <alexghiti@...osinc.com>
To: Paul Walmsley <paul.walmsley@...ive.com>, 
 Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, 
 Alexandre Ghiti <alex@...ti.fr>
Cc: linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org, 
 stable@...r.kernel.org, Alexandre Ghiti <alexghiti@...osinc.com>
Subject: [PATCH] riscv: Use an atomic xchg in pudp_huge_get_and_clear()

Make sure we return the right pud value and not a value that could
have been overwritten in between by a different core.

Fixes: c3cc2a4a3a23 ("riscv: Add support for PUD THP")
Cc: stable@...r.kernel.org
Signed-off-by: Alexandre Ghiti <alexghiti@...osinc.com>
---
Note that this will conflict with
https://lore.kernel.org/linux-riscv/20250625063753.77511-1-ajd@linux.ibm.com/
if applied after 6.17.
---
 arch/riscv/include/asm/pgtable.h | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
index 91697fbf1f9013005800f713797e4b6b1fc8d312..e69346307e78608dd98d8b7a77b7063c333448ee 100644
--- a/arch/riscv/include/asm/pgtable.h
+++ b/arch/riscv/include/asm/pgtable.h
@@ -942,6 +942,17 @@ static inline int pudp_test_and_clear_young(struct vm_area_struct *vma,
 	return ptep_test_and_clear_young(vma, address, (pte_t *)pudp);
 }
 
+#define __HAVE_ARCH_PUDP_HUGE_GET_AND_CLEAR
+static inline pud_t pudp_huge_get_and_clear(struct mm_struct *mm,
+					    unsigned long address, pud_t *pudp)
+{
+	pud_t pud = __pud(atomic_long_xchg((atomic_long_t *)pudp, 0));
+
+	page_table_check_pud_clear(mm, pud);
+
+	return pud;
+}
+
 static inline int pud_young(pud_t pud)
 {
 	return pte_young(pud_pte(pud));

---
base-commit: 62950c35a515743739e3d863eac25c20a5bd1613
change-id: 20250814-dev-alex-thp_pud_xchg-8153c313d946

Best regards,
-- 
Alexandre Ghiti <alexghiti@...osinc.com>