From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id A6252EA854A for ; Mon, 9 Mar 2026 02:57:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: MIME-Version:References:In-Reply-To:Message-Id:Date:Subject:Cc:To:From: Reply-To:Content-Type:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=dV6rN6wJGEGhX76L1tLL+S50brKK/SeiWBmYpmhZ6W8=; b=R64tN8gY4Do6x/Nyfa3cNEXkGE YxV2qk1qdowIhSvFY0+Rjowu4ogt9CVSRKygJ1F0PcD2Fa5e1+xzdIUnB4kPc3ySQML1e/DPAjwcu ychSjeEqskX3eL0cflfswOXWL808uOgtItmxVP/FH03OuTxvtQlURLdzQYYgE1n49aY+S4KOnCYJU +jZ29uHnE4qxkWtx2CVjeh9/hdRcNIbGn8xA2WzQkLH5cJ1YFwrspjuM+uOjWLUfldAyKMsfr+AKq FflbvSvR8JlpnzQ2uUhmxZLrmoJZchCNroWQzP8m4c8DLGJwFqmff/0nVFaWMn11GcYDGDu2nQgV0 pbPP+RVQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1vzQoO-00000006ZGk-0qr5; Mon, 09 Mar 2026 02:57:40 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1vzQoJ-00000006ZFX-39Dl for linux-arm-kernel@lists.infradead.org; Mon, 09 Mar 2026 02:57:38 +0000 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 E26961D15; Sun, 8 Mar 2026 19:57:26 -0700 (PDT) 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 A16943F694; Sun, 8 Mar 2026 19:57:31 -0700 (PDT) From: Anshuman Khandual To: linux-arm-kernel@lists.infradead.org Cc: Anshuman Khandual , Catalin Marinas , Will Deacon , Ryan Roberts , David Hildenbrand , Yang Shi , Christoph Lameter , linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: [PATCH V5 1/2] arm64/mm: Enable batched TLB flush in unmap_hotplug_range() Date: Mon, 9 Mar 2026 02:57:24 +0000 Message-Id: <20260309025725.455004-2-anshuman.khandual@arm.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20260309025725.455004-1-anshuman.khandual@arm.com> References: <20260309025725.455004-1-anshuman.khandual@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260308_195735_889066_DAF990E8 X-CRM114-Status: GOOD ( 16.63 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org During a memory hot remove operation, 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: David Hildenbrand (Arm) Reviewed-by: Ryan Roberts Signed-off-by: Ryan Roberts Signed-off-by: Anshuman Khandual --- arch/arm64/mm/mmu.c | 36 ++++++++++++++++++++---------------- 1 file changed, 20 insertions(+), 16 deletions(-) diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c index a6a00accf4f9..5dbf988120c8 100644 --- a/arch/arm64/mm/mmu.c +++ b/arch/arm64/mm/mmu.c @@ -1458,10 +1458,14 @@ static void unmap_hotplug_pte_range(pmd_t *pmdp, unsigned long addr, 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) { + /* CONT blocks are not supported in the vmemmap */ + WARN_ON(pte_cont(pte)); + flush_tlb_kernel_range(addr, addr + PAGE_SIZE); free_hotplug_page_range(pte_page(pte), PAGE_SIZE, altmap); + } + /* unmap_hotplug_range() flushes TLB for !free_mapped */ } while (addr += PAGE_SIZE, addr < end); } @@ -1482,15 +1486,14 @@ static void unmap_hotplug_pmd_range(pud_t *pudp, unsigned long addr, WARN_ON(!pmd_present(pmd)); if (pmd_sect(pmd)) { pmd_clear(pmdp); - - /* - * One TLBI should be sufficient here as the PMD_SIZE - * range is mapped with a single block entry. - */ - flush_tlb_kernel_range(addr, addr + PAGE_SIZE); - if (free_mapped) + if (free_mapped) { + /* CONT blocks are not supported in the vmemmap */ + WARN_ON(pmd_cont(pmd)); + flush_tlb_kernel_range(addr, addr + PMD_SIZE); free_hotplug_page_range(pmd_page(pmd), PMD_SIZE, altmap); + } + /* unmap_hotplug_range() flushes TLB for !free_mapped */ continue; } WARN_ON(!pmd_table(pmd)); @@ -1515,15 +1518,12 @@ static void unmap_hotplug_pud_range(p4d_t *p4dp, unsigned long addr, WARN_ON(!pud_present(pud)); if (pud_sect(pud)) { pud_clear(pudp); - - /* - * One TLBI should be sufficient here as the PUD_SIZE - * range is mapped with a single block entry. - */ - flush_tlb_kernel_range(addr, addr + PAGE_SIZE); - if (free_mapped) + if (free_mapped) { + flush_tlb_kernel_range(addr, addr + PUD_SIZE); free_hotplug_page_range(pud_page(pud), PUD_SIZE, altmap); + } + /* unmap_hotplug_range() flushes TLB for !free_mapped */ continue; } WARN_ON(!pud_table(pud)); @@ -1553,6 +1553,7 @@ static void unmap_hotplug_p4d_range(pgd_t *pgdp, unsigned long addr, static void unmap_hotplug_range(unsigned long addr, unsigned long end, bool free_mapped, struct vmem_altmap *altmap) { + unsigned long start = addr; unsigned long next; pgd_t *pgdp, pgd; @@ -1574,6 +1575,9 @@ 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 = next, addr < end); + + if (!free_mapped) + flush_tlb_kernel_range(start, end); } static void free_empty_pte_table(pmd_t *pmdp, unsigned long addr, -- 2.30.2