From nobody Sat Feb 7 08:27:48 2026 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 610EA34AB01; Tue, 3 Feb 2026 13:04:07 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770123849; cv=none; b=k38cGD/tnApjwqiM3RNuBgxTzv4tUyIXkxx2+JQWI2v3I2shv8wIcMLWRqQDFmWXS1bPifTDGDr0j2q7Uz5D80+1ptflr3USl7vNhankUG7Y67UOW+TOhMVRoAp0XmnDfi3NVe0zMaHWCm92Hmi72a9v3YOHjJMkzOr3ZNe16MI= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770123849; c=relaxed/simple; bh=jEHkOLY6CrcuIiBUHU54N/UJHObZRXh2vYjIqj+zaIM=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=rQjfWtO3B110P2QZSNT/l/4pE/VRegPp2EjkSSYvA/arXLoIkjWM3iwnpbi4h/j4+FDNQ8Iia2AW5AuxMeWFmcvogacLfQ1ZFHV53gH++rjtgoxQ5l3CyC/cr9r5BB98S3AXOw8ggzz/sX8ZtNqDgfB5n8+eqLmKwqvMFZe7NNk= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 5D7C0497; Tue, 3 Feb 2026 05:04:00 -0800 (PST) Received: from ergosum.cambridge.arm.com (ergosum.cambridge.arm.com [10.1.196.45]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 68C763F632; Tue, 3 Feb 2026 05:04:05 -0800 (PST) From: Anshuman Khandual To: linux-arm-kernel@lists.infradead.org Cc: Anshuman Khandual , Catalin Marinas , Will Deacon , Ryan Roberts , Yang Shi , Christoph Lameter , linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: [PATCH V2 1/2] arm64/mm: Enable batched TLB flush in unmap_hotplug_range() Date: Tue, 3 Feb 2026 13:03:47 +0000 Message-Id: <20260203130348.612150-2-anshuman.khandual@arm.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20260203130348.612150-1-anshuman.khandual@arm.com> References: <20260203130348.612150-1-anshuman.khandual@arm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" During a memory hot remove operartion both linear and vmemmap mappings for the memory range being removed, get unmapped via unmap_hotplug_range() but mapped pages get freed only for vmemmap mapping. This is just a sequential operation where each table entry gets cleared, followed by a leaf specific TLB flush, and then followed by memory free operation when applicable. This approach was simple and uniform both for vmemmap and linear mappings. But linear mapping might contain CONT marked block memory where it becomes necessary to first clear out all entire in the range before a TLB flush. This is as per the architecture requirement. Hence batch all TLB flushes during the table tear down walk and finally do it in unmap_hotplug_range(). Prior to this fix, it was hypothetically possible for a speculative access to a higher address in the contiguous block to fill the TLB with shattered entries for the entire contiguous range after a lower address had already been cleared and invalidated. Due to the table entries being shattered, the subsequent TLB invalidation for the higher address would not then clear the TLB entries for the lower address, meaning stale TLB entries could persist. Besides it also helps in improving the performance via TLBI range operation along with reduced synchronization instructions. The time spent executing unmap_hotplug_range() improved 97% measured over a 2GB memory hot removal in KVM guest. This scheme is not applicable during vmemmap mapping tear down where memory needs to be freed and hence a TLB flush is required after clearing out page table entry. Cc: Catalin Marinas Cc: Will Deacon Cc: linux-arm-kernel@lists.infradead.org Cc: linux-kernel@vger.kernel.org Closes: https://lore.kernel.org/all/aWZYXhrT6D2M-7-N@willie-the-truck/ Fixes: bbd6ec605c0f ("arm64/mm: Enable memory hot remove") Cc: stable@vger.kernel.org Reviewed-by: Ryan Roberts Signed-off-by: Ryan Roberts Signed-off-by: Anshuman Khandual --- arch/arm64/mm/mmu.c | 81 +++++++++++++++++++++++++++++++++++++-------- 1 file changed, 67 insertions(+), 14 deletions(-) diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c index 8e1d80a7033e..8ec8a287aaa1 100644 --- a/arch/arm64/mm/mmu.c +++ b/arch/arm64/mm/mmu.c @@ -1458,10 +1458,32 @@ static void unmap_hotplug_pte_range(pmd_t *pmdp, un= signed long addr, =20 WARN_ON(!pte_present(pte)); __pte_clear(&init_mm, addr, ptep); - flush_tlb_kernel_range(addr, addr + PAGE_SIZE); - if (free_mapped) + if (free_mapped) { + /* + * If page is part of an existing contiguous + * memory block, individual TLB invalidation + * here would not be appropriate. Instead it + * will require clearing all entries for the + * memory block and subsequently a TLB flush + * for the entire range. + */ + WARN_ON(pte_cont(pte)); + + /* + * TLB flush is essential for freeing memory. + */ + flush_tlb_kernel_range(addr, addr + PAGE_SIZE); free_hotplug_page_range(pte_page(pte), PAGE_SIZE, altmap); + } + + /* + * TLB flush is batched in unmap_hotplug_range() + * for the entire range, when memory need not be + * freed. Besides linear mapping might have CONT + * blocks where TLB flush needs to be done after + * clearing all relevant entries. + */ } while (addr +=3D PAGE_SIZE, addr < end); } =20 @@ -1482,15 +1504,32 @@ static void unmap_hotplug_pmd_range(pud_t *pudp, un= signed long addr, WARN_ON(!pmd_present(pmd)); if (pmd_sect(pmd)) { pmd_clear(pmdp); + if (free_mapped) { + /* + * If page is part of an existing contiguous + * memory block, individual TLB invalidation + * here would not be appropriate. Instead it + * will require clearing all entries for the + * memory block and subsequently a TLB flush + * for the entire range. + */ + WARN_ON(pmd_cont(pmd)); + + /* + * TLB flush is essential for freeing memory. + */ + flush_tlb_kernel_range(addr, addr + PMD_SIZE); + free_hotplug_page_range(pmd_page(pmd), + PMD_SIZE, altmap); + } =20 /* - * One TLBI should be sufficient here as the PMD_SIZE - * range is mapped with a single block entry. + * TLB flush is batched in unmap_hotplug_range() + * for the entire range, when memory need not be + * freed. Besides linear mapping might have CONT + * blocks where TLB flush needs to be done after + * clearing all relevant entries. */ - flush_tlb_kernel_range(addr, addr + PAGE_SIZE); - if (free_mapped) - free_hotplug_page_range(pmd_page(pmd), - PMD_SIZE, altmap); continue; } WARN_ON(!pmd_table(pmd)); @@ -1515,15 +1554,20 @@ static void unmap_hotplug_pud_range(p4d_t *p4dp, un= signed long addr, WARN_ON(!pud_present(pud)); if (pud_sect(pud)) { pud_clear(pudp); + if (free_mapped) { + /* + * TLB flush is essential for freeing memory. + */ + flush_tlb_kernel_range(addr, addr + PUD_SIZE); + free_hotplug_page_range(pud_page(pud), + PUD_SIZE, altmap); + } =20 /* - * One TLBI should be sufficient here as the PUD_SIZE - * range is mapped with a single block entry. + * TLB flush is batched in unmap_hotplug_range() + * for the entire range, when memory need not be + * freed. */ - flush_tlb_kernel_range(addr, addr + PAGE_SIZE); - if (free_mapped) - free_hotplug_page_range(pud_page(pud), - PUD_SIZE, altmap); continue; } WARN_ON(!pud_table(pud)); @@ -1553,6 +1597,7 @@ static void unmap_hotplug_p4d_range(pgd_t *pgdp, unsi= gned long addr, static void unmap_hotplug_range(unsigned long addr, unsigned long end, bool free_mapped, struct vmem_altmap *altmap) { + unsigned long start =3D addr; unsigned long next; pgd_t *pgdp, pgd; =20 @@ -1574,6 +1619,14 @@ static void unmap_hotplug_range(unsigned long addr, = unsigned long end, WARN_ON(!pgd_present(pgd)); unmap_hotplug_p4d_range(pgdp, addr, next, free_mapped, altmap); } while (addr =3D next, addr < end); + + /* + * Batched TLB flush only for linear mapping which + * might contain CONT blocks, and does not require + * freeing up memory as well. + */ + if (!free_mapped) + flush_tlb_kernel_range(start, end); } =20 static void free_empty_pte_table(pmd_t *pmdp, unsigned long addr, --=20 2.30.2