From: Anshuman Khandual <anshuman.khandual@arm.com>
Date: Fri, 26 Jun 2026 01:28:45 +0000 (+0100)
Subject: arm64/mm: Optimize TLB flush in unmap_hotplug_[pmd|pud]_range()
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=ff4c5a0de1f2ef7737a8688a86e19301e567020d;p=thirdparty%2Fkernel%2Flinux.git

arm64/mm: Optimize TLB flush in unmap_hotplug_[pmd|pud]_range()

Commit 48478b9f7913 ("arm64/mm: Enable batched TLB flush in
unmap_hotplug_range") inadvertently introduced redundant TLB
invalidation when clearing a block entry, resulting in unnecessary
broadcast invalidation on CPUs without support for range-based
invalidation.

Re-introduce the old behaviour, along with some expanded comments to
help people working in this area next time around.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Reported-by: Ben Hutchings <ben@decadent.org.uk>
Closes: https://lore.kernel.org/all/b0d5836032ce3135bfc473f6bff791306d086925.camel@decadent.org.uk/
Fixes: 48478b9f7913 ("arm64/mm: Enable batched TLB flush in unmap_hotplug_range()")
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
Reviewed-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
[will: Reword comments and commit message]
Signed-off-by: Will Deacon <will@kernel.org>
---

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index f2be501468ce..a25d8beacc83 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -1515,7 +1515,13 @@ static void unmap_hotplug_pmd_range(pud_t *pudp, unsigned long addr,
 			if (free_mapped) {
 				/* CONT blocks are not supported in the vmemmap */
 				WARN_ON(pmd_cont(pmd));
-				flush_tlb_kernel_range(addr, addr + PMD_SIZE);
+				/*
+				 * Invalidating a block entry requires just
+				 * a single overlapping TLB invalidation,
+				 * so limit the range of the flush to a single
+				 * page.
+				 */
+				flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
 				free_hotplug_page_range(pmd_page(pmd),
 							PMD_SIZE, altmap);
 			}
@@ -1545,7 +1551,8 @@ static void unmap_hotplug_pud_range(p4d_t *p4dp, unsigned long addr,
 		if (pud_leaf(pud)) {
 			pud_clear(pudp);
 			if (free_mapped) {
-				flush_tlb_kernel_range(addr, addr + PUD_SIZE);
+				/* See comment in unmap_hotplug_pmd_range(). */
+				flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
 				free_hotplug_page_range(pud_page(pud),
 							PUD_SIZE, altmap);
 			}