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 B4CBBF30946 for ; Thu, 5 Mar 2026 12:37:52 +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: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=WEpe7E4Byt5MfzVyHGj5LKfw000c+UL9SUdPrf0zlDU=; b=MN1XKAVl91OZZ3DzN1YsORcCM0 UgtDTPqEr4eNmH+ud0RYaqO2qqmUomrKDDpj/YTV5kHj/u9fPxo9daT7Sd3igXaifEM7S8iHbYpzv 89NswBsuz0ZRplRBdU+vuDpgat6ebMd0DiWYMcXiXG3dRoc6YGztR4AnaPycR0GIT4Auc5Faaw5+6 TX16G192U9IF+GlA3qQHEoZv+IFot8J7iamMnjmIUZ8m4wJRpNBA5EU2vhO2pbQTGpc0OutlOM7zK 42xVGXGYppRo0tubUo9+JX1gGa24LyizrJqa/LGK6zE8DJJDWAgFCO/JbtUYMP2ZeC9eqITH95Abe KLbnzHBw==; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260305_043745_409751_FA7D97F8 X-CRM114-Status: GOOD ( 16.32 ) 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 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