From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id ABC3B36682A; Thu, 5 Mar 2026 12:39:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772714357; cv=none; b=XpMxf4VKxC3eN4OeBXYhTIO4OZbTCTqkt9+LNloWaTztRxGcm3vDk51n9EyPrYRlwfhPptgDYNtEyhJk0n3fcG8dHPdwX5/JQ8Kmry1hNDZ30uV4kD8YDM0tIx9Pm2szZRAbDMBV6AZLLPLE6+whlTOTpjYh7nQpKTjnmL+9rXo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772714357; c=relaxed/simple; bh=KHW4zGFxdwtgS6DZ4KhYyjuMBJUABIaJ1Yd4ZcE2WkU=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=P7PrWtJ+0kHTFWpeelOL3Bob2JdCsTGBozRmvRVk19v9i/ETjUxxLiaGwNZ4ukLfiev3skbEv9yhb1E77SB0og/zGosxc9lGfGzDBNse79chuDlCFdQZMgBOqMp/ttIfgpgdGqLEwSp6zKErLa5qy3fztYDT6DpFQ5f7dKulWzY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=SK8khnZE; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="SK8khnZE" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B7F75C116C6; Thu, 5 Mar 2026 12:39:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772714357; bh=KHW4zGFxdwtgS6DZ4KhYyjuMBJUABIaJ1Yd4ZcE2WkU=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=SK8khnZEPjBqHDibVqZgldRd8kodqYHKeDVbUmohIiR8IWxOdaBzkdpRq51LctnYK iSUUsL179ubvsOSrJhfT3BAw7HQhKc/auJ7YF476GEGuW8hIKu30z1RXE5suh73xFk OmUDRSe87FrND8tFRvPlxa+yYJY0+O0UWKPanNyv8u6mHCb+E57Aa8bUtS1X1qqb3u Cgj9jdifKdvtjuLtU0bxEnhLAazWQJ9XIpPnWZNZZ6VAtvDpRaw+GAQK5TwwuMM/Y8 zhLiCMcv67AY+pjXqPlXtjpCDNyzU7ydr4842wUo8by0RQMD5q/qPjepDHy/Ri9Rbb RF8uWHcGrdKzA== Message-ID: <8443cc2a-fd39-4af8-b3cc-370f6987b85c@kernel.org> Date: Thu, 5 Mar 2026 13:39:11 +0100 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH V4 1/2] arm64/mm: Enable batched TLB flush in unmap_hotplug_range() To: Anshuman Khandual , linux-arm-kernel@lists.infradead.org Cc: Catalin Marinas , Will Deacon , Ryan Roberts , Yang Shi , Christoph Lameter , linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20260305053148.3765710-1-anshuman.khandual@arm.com> <20260305053148.3765710-2-anshuman.khandual@arm.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 3/5/26 06:31, Anshuman Khandual wrote: > 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: Ryan Roberts > Signed-off-by: Ryan Roberts > Signed-off-by: Anshuman Khandual > --- > arch/arm64/mm/mmu.c | 46 +++++++++++++++++++++++++++++---------------- > 1 file changed, 30 insertions(+), 16 deletions(-) > > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c > index a6a00accf4f9..f7ccda22d39e 100644 > --- a/arch/arm64/mm/mmu.c > +++ b/arch/arm64/mm/mmu.c > @@ -1458,10 +1458,18 @@ 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 > + */ Same nit as on patch #2, /* CONT blocks are not supported in the vmemmap */ Same for the other comments. Thanks! Reviewed-by: David Hildenbrand (Arm) -- Cheers, David