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 B0FE339F18E for ; Thu, 5 Mar 2026 12:37:44 +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=1772714264; cv=none; b=YNXvV9wFKUKIvHtuZKih2tQXmmEYO9JVNKny7jEl4wtPMlERMAYspxpkUG53uHoaG6mJiSciYg4Ddfi14iZPXQGAPkMqk3QAspYSdraoDRIn9PEdQCMkB79mO2z4iWIlj1NOPbHkl0Azk8za87PJR2lO59EyEBxT3QCudqJqRiA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772714264; c=relaxed/simple; bh=qmwOM88pig4Nq4HUd0fMB96N+Rr3BRS1u/CGhx+ArjI=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=gn9Ss3mTb3iK6CaYOGUXqibWuiaQG5XHLlcJfYLSkqwbTRyHYTaoZwBMC4mkyWVtT0N5GkuErguX3hwe5utj3xl0XbTG/XQtfO30jAxPShJReiC5ARmLgfTXQfOQVwLS/THHoSV7a1p7JodmzODu0w5d0C/aDwOXZODRZBdvkwE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=leZ8v1Me; 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="leZ8v1Me" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2E42BC2BC87; Thu, 5 Mar 2026 12:37:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772714264; bh=qmwOM88pig4Nq4HUd0fMB96N+Rr3BRS1u/CGhx+ArjI=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=leZ8v1MeqIZmr7oHBVyoEp4LhKcAuvYKGR9d+WtlSNyyCRoJfldu3qCsoz30nufTk d+M+6yuDbmu0o+PYUprzSbWXuV1jQbjJsIgDhHXmq7rBpw8ZYGrg0Z435MR2nzc7Cy OkLNQQ3qvTaSNdsw6aD1dmrFIOLodOjCbVECv2PjMEZslnZvt3FB2LZ4hY5sSBvXdJ m5RqqN1avGdCJXDYH0nQrUprhD8g+27bG9dQT8/PbjbvdJvjnlrCckTJDcT3irTPqV V4gISkR7n6YuX02lioSkjFJEeqxfdqPpB6dMdXxCjmkRD3UpeXr0m+KClkLRp1lwEA E9K5wRVtA9iIQ== Message-ID: Date: Thu, 5 Mar 2026 13:37:38 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH V4 2/2] arm64/mm: Reject memory removal that splits a kernel leaf mapping 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 References: <20260305053148.3765710-1-anshuman.khandual@arm.com> <20260305053148.3765710-3-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: > Linear and vmemmap mappings that get torn down during a memory hot remove > operation might contain leaf level entries on any page table level. If the > requested memory range's linear or vmemmap mappings falls within such leaf > entries, new mappings need to be created for the remaining memory mapped on > the leaf entry earlier, following standard break before make aka BBM rules. > But kernel cannot tolerate BBM and hence remapping to fine grained leaves > would not be possible on systems without BBML2_NOABORT. > > Currently memory hot remove operation does not perform such restructuring, > and so removing memory ranges that could split a kernel leaf level mapping > need to be rejected. > > While memory_hotplug.c does appear to permit hot removing arbitrary ranges > of memory, the higher layers that drive memory_hotplug (e.g. ACPI, virtio, > ...) all appear to treat memory as fixed size devices. So it is impossible > to hot unplug a different amount than was previously hot plugged, and hence > we should never see a rejection in practice, but adding the check makes us > robust against a future change. > > Cc: Catalin Marinas > Cc: Will Deacon > Cc: linux-arm-kernel@lists.infradead.org > Cc: linux-kernel@vger.kernel.org > Link: https://lore.kernel.org/all/aWZYXhrT6D2M-7-N@willie-the-truck/ > Reviewed-by: Ryan Roberts > Suggested-by: Ryan Roberts > Signed-off-by: Anshuman Khandual > --- [...] > + > + /* > + * PFN range's linear map edges are leaf entry aligned > + */ Nit: single-line comments are usually written as /* ... */ > + start = __phys_to_virt(phys_start); > + end = __phys_to_virt(phys_end); > + if (addr_splits_kernel_leaf(start) || addr_splits_kernel_leaf(end)) { > + pr_warn("[%lx %lx] splits a leaf entry in linear map\n", > + phys_start, phys_end); > + return false; > + } > + > + /* > + * PFN range's vmemmap edges are leaf entry aligned > + */ Dito. LGTM, thanks! Acked-by: David Hildenbrand (Arm) -- Cheers, David