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 16818371054 for ; Thu, 5 Mar 2026 12:39:47 +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=1772714387; cv=none; b=JH+lP2+H/oTyPsDejSCIi7czoS5HpPclUGro9qOGUF1ssJbeyMF3qd4nF9nLAovnYqX11iQkG8fYjSYBtoqsNfdUFg26zBSgMv4H6AGIwxFPwBxzwnwRj1eK36feF0Wf/372pjCz+tW27pzIjzoK3PLoXi8rlsY43bLr+m3doF8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772714387; c=relaxed/simple; bh=NHjvP5Apmcg681KyizLkhQcHDwKR9Nf0s0Y484PlvsA=; h=Message-ID:Date:MIME-Version:Subject:From:To:Cc:References: In-Reply-To:Content-Type; b=RuJgwC0HK+YBzjjRAn3mpZWrezsSHpD4JVnRtLc8mx1aMoBhFFf9ZHqsPCHhzlRcClzQT8hv5m3vTlnC5DXNoblqhP4nnFs5f7uWRSjZaflDLXpPK7LTOmIUMKRfTjQK5SzH3KvA88xQI2VG+NHSZwuY3YKg0R2E6ZbmjeY4vFU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=P9ZCpTm1; 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="P9ZCpTm1" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8AEA2C19423; Thu, 5 Mar 2026 12:39:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772714387; bh=NHjvP5Apmcg681KyizLkhQcHDwKR9Nf0s0Y484PlvsA=; h=Date:Subject:From:To:Cc:References:In-Reply-To:From; b=P9ZCpTm1C4pe2uAMW7UXulE7Cj+noO09jxkI0IAcsCHXDK+ESrzixqBiWF1lNG3JS B3UUBAEApJ0pH9jMpMJUF3hu9+uevGNBlHRzCZ+9zrNMg09LhEw6sVVj5pwCi3Vo8/ dLRxaXLPK0V4srgxVV1s/M5AIWmLyPmbr+FrTTOv8hoqjZZSY/YE0dh5n2Z3V5gyfX W/wze6nPqQoKPpl3ADdqw7zgRNw+oYa1kclyeH6hULDs6IiX04jDTI19C5hI4KJO34 FWSiKcFHzvK2Pa5n506ZfD7toKcC0yj0cTnMzr3zI+QUAt16ywy3mz5DeFppf/IkJO bVqQeepibU1eQ== Message-ID: <3884dd41-8ab1-45ee-8daa-198384d59c20@kernel.org> Date: Thu, 5 Mar 2026 13:39:41 +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 From: "David Hildenbrand (Arm)" 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> Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 3/5/26 13:37, David Hildenbrand (Arm) wrote: > 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) > In fact, Reviewed-by: David Hildenbrand (Arm) :) -- Cheers, David