linux-kernel - [PATCH] arm64/mm: Ensure adequate HUGE_MAX

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Message-Id: <20241202064407.53807-1-anshuman.khandual@arm.com>
Date: Mon,  2 Dec 2024 12:14:07 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: linux-arm-kernel@...ts.infradead.org
Cc: Anshuman Khandual <anshuman.khandual@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	Ard Biesheuvel <ardb@...nel.org>,
	Ryan Roberts <ryan.roberts@....com>,
	Mark Rutland <mark.rutland@....com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] arm64/mm: Ensure adequate HUGE_MAX_HSTATE

This asserts that HUGE_MAX_HSTATE is sufficient enough preventing potential
hugetlb_max_hstate runtime overflow in hugetlb_add_hstate() thus triggering
a BUG_ON() there after.

Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Will Deacon <will@...nel.org>
Cc: Ard Biesheuvel <ardb@...nel.org>
Cc: Ryan Roberts <ryan.roberts@....com>
Cc: Mark Rutland <mark.rutland@....com>
Cc: linux-arm-kernel@...ts.infradead.org
Cc: linux-kernel@...r.kernel.org
Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
---
This patch applies on v6.13-rc1

 arch/arm64/mm/hugetlbpage.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
index 3215adf48a1b..98a2a0e64e25 100644
--- a/arch/arm64/mm/hugetlbpage.c
+++ b/arch/arm64/mm/hugetlbpage.c
@@ -519,6 +519,18 @@ pte_t huge_ptep_clear_flush(struct vm_area_struct *vma,
 
 static int __init hugetlbpage_init(void)
 {
+	/*
+	 * HugeTLB pages are supported on maximum four page table
+	 * levels (PUD, CONT PMD, PMD, CONT PTE) for a given base
+	 * page size, corresponding to hugetlb_add_hstate() calls
+	 * here.
+	 *
+	 * HUGE_MAX_HSTATE should at least match maximum supported
+	 * HugeTLB page sizes on the platform. Any new addition to
+	 * supported HugeTLB page sizes will also require changing
+	 * HUGE_MAX_HSTATE as well.
+	 */
+	BUILD_BUG_ON(HUGE_MAX_HSTATE < 4);
 	if (pud_sect_supported())
 		hugetlb_add_hstate(PUD_SHIFT - PAGE_SHIFT);
 
-- 
2.30.2