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 7B57037CD56 for ; Tue, 3 Mar 2026 09:00:53 +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=1772528453; cv=none; b=YCJEuknojDqi8oc1ep8jELoHQ62shmXrSSzeoPwr7yHr/SfYzMBR/iQywktFXHV5n6qAi2l3DFDbwrnvbrke0HibhG1+kq3zLh6SrsfgXHiTkzYEIqBMoRiU1XbuxkSGHK3SgwTAA3gMGVen4cxEkLZlyrDHb288p6eVaCdBoyA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772528453; c=relaxed/simple; bh=3dVrtbk4cGUF1pWmZh+6baPm+xvADcchrMO5vTV2IvE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=KD9KhbowcAAfvXmQEralkPUetELZA0D/NqJP95TYen38PUr6fMjj5MXH7xkkqeDEy1MNSAqBVgrIu1bVdp6qUsbabFTMYR7mCYIexqNYKW6RItiPV0UILF9Vc3MEiXHgEmZrEW7TKgDBpnrg0wtqh+E99wdE91qDjHRupkRRiuk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ccnNdfoJ; 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="ccnNdfoJ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E1713C116C6; Tue, 3 Mar 2026 09:00:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772528453; bh=3dVrtbk4cGUF1pWmZh+6baPm+xvADcchrMO5vTV2IvE=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=ccnNdfoJ5l+jc5QqQZQ2k0gHRvVY+IvHBiVv77pmPxkvbGv1cDMPgODVvy8IYbq3y HsmtdmRbBWVGoVLp0+JZ6vq8ImAdepWoGX49zoXrDhEl9sE59TNSZyTvfbTn83g1UA 6ly0Nu+su+M+7zKfFuBHxd1vGp0hMCdKGnZMk1lyE3YyLSgz5IeNkRL8I/hi164drR xt/jXBwfAD9PerGPUWZrumQHMA028QFDQfXBwa9G9PjQcOzA6uShTxuQ8jsTxQGMwk 3si5ZOHuIkj5xpHufNWARGA28uRH6+COtQCpM4dWRsfMJEf0S2i+dp1k6vzUdaI1IT OKQccE+kZayGQ== Message-ID: <05e6034d-3493-4961-a97d-a80fff78289b@kernel.org> Date: Tue, 3 Mar 2026 10:00:49 +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 V3 2/2] arm64/mm: Reject memory removal that splits a kernel leaf mapping To: Anshuman Khandual , linux-arm-kernel@lists.infradead.org Cc: mark.rutland@arm.com, Catalin Marinas , Will Deacon , Ryan Roberts , Yang Shi , Christoph Lameter , linux-kernel@vger.kernel.org References: <20260224062423.972404-1-anshuman.khandual@arm.com> <20260224062423.972404-3-anshuman.khandual@arm.com> <6eee7f14-c3f2-4e16-b713-65c2ea141457@kernel.org> <2d07e814-a7a3-4cec-8a59-158420bde1f2@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 >> I can understand the desire for this check, but I am confused about Fixes: > > Probably nothing is broken now I guess but the original memory hot remove > patch should have taken care of this scenario. Although don't have strong > opinions either way. We could drop both "Fixes" and "Closes" tags here if > that is preferred. > We tend to only tag actual fixes. If we consider this a possible fix, we should ask ourselves whether this would be stable material. ... >>> + return false; >>> + >>> + pgdp = pgd_offset_k(addr); >>> + pgd = pgdp_get(pgdp); >>> + if (!pgd_present(pgd)) >>> + return false; >> >> How could we end up with non-present areas in a range we hotplugged earlier? > > We might not in reality but in order to be sure just an additional protection. I'm rather wondering if this would indicate a real bug somewhere else that we would silently swallow. Anyhow, no real preference from my side, just something I considered weird. [...] >>> + >>> +static bool can_unmap_without_split(unsigned long pfn, unsigned long nr_pages) >>> +{ >>> + unsigned long phys_start, phys_end, size, start, end; >>> + >>> + phys_start = PFN_PHYS(pfn); >>> + phys_end = phys_start + nr_pages * PAGE_SIZE; >>> + >>> + /* >>> + * PFN range's linear map edges are leaf entry aligned >>> + */ >>> + 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 >>> + */ >>> + size = nr_pages * sizeof(struct page); >>> + start = (unsigned long)pfn_to_page(pfn); >>> + end = start + size; >> >> As arm64 cannot be used with CONFIG_SPARSEMEM (only with >> CONFIG_SPARSEMEM_VMEMMAP, as it sets SPARSEMEM_VMEMMAP_ENABLE), >> I think you can just do Just to clarify: What I meant here is: with CONFIG_SPARSEMEM but without CONFIG_SPARSEMEM_VMEMMAP. -- Cheers, David