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 189E1C4828F for ; Wed, 7 Feb 2024 11:13:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=LpcnYBmEuT1CfwyRCOxiLUpXKhYKXSZFa+2wwoewQO0=; b=rMlXExU1nZhnnf 8jbOfvkJK0biMxcsl6D5f/2TrBqDa0glz25mE95f6nfZg4BLpPWFtnYD9tTSXSQcqUuZZwCHPkxAj iMvouGwn62xM4TLDtpbkpRC6kvCOCm3/ZWTRWXkeNK4bFWr+4rub2wD45MNccDHTB48okZlUv9udx 2y5q+03W1N04CgcI3KaiFxDYgTC/Ml4rA7KTQbhu4D/rCT3TYNgWxmpgWBop3BFiEGng1KT8OiM8x vcQc94hMQuYbzKDA3g9UbVIni0P6AkL1X32Ij99N1t08HMVwAcYderlBqxF4hEpGGldVlaCPkEOwk zysaQP9rJdl67SEh96cQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1rXfrU-0000000ARpd-1jIg; Wed, 07 Feb 2024 11:13:04 +0000 Received: from sin.source.kernel.org ([145.40.73.55]) by bombadil.infradead.org with esmtps (Exim 4.97.1 #2 (Red Hat Linux)) id 1rXfrR-0000000ARok-24iC for linux-arm-kernel@lists.infradead.org; Wed, 07 Feb 2024 11:13:02 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sin.source.kernel.org (Postfix) with ESMTP id 419CDCE1381; Wed, 7 Feb 2024 11:12:59 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6D42EC433F1; Wed, 7 Feb 2024 11:12:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1707304378; bh=Wdwlj8End667TasRIp745gWvCi1r+Z+ho/QV9RjE1iM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=BR7gVvcBwGGbvbZfh7xizzOqoGFPTI0JQWsV7ndm9o6m3Ea8vwZVbv/9ygor6Vx4W qZU5i/hgHxS9F7vgiKb3m/YM9C/JQbILhIG58u0xr8GwjEynXC2o3FUpkX47vTzBi8 RT9oYPYnBzc0lcB6QUQLHD0HHuF3CLlRn8+0pMlp4pHpTrSzJvCK8c833CQRRJocLl GFhSagN7yVuG0QqORcjvg+FhmUtwd9Sj+LddWIN4v+MloroBcWy7FADQHVWahafU0g G3+NbfE6o/szBGOVSMw+nHdIA2eEeqzrlm5STgTFp38hcoaDdLcmo9CWKbu4rEa89X xaS/xIlnSDqzg== Date: Wed, 7 Feb 2024 11:12:52 +0000 From: Will Deacon To: Nanyong Sun Cc: Catalin Marinas , mike.kravetz@oracle.com, muchun.song@linux.dev, akpm@linux-foundation.org, anshuman.khandual@arm.com, willy@infradead.org, wangkefeng.wang@huawei.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v3 0/3] A Solution to Re-enable hugetlb vmemmap optimize Message-ID: <20240207111252.GA22167@willie-the-truck> References: <20240113094436.2506396-1-sunnanyong@huawei.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240207_031301_736651_5F57C30B X-CRM114-Status: GOOD ( 22.66 ) 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: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Sat, Jan 27, 2024 at 01:04:15PM +0800, Nanyong Sun wrote: > > On 2024/1/26 2:06, Catalin Marinas wrote: > > On Sat, Jan 13, 2024 at 05:44:33PM +0800, Nanyong Sun wrote: > > > HVO was previously disabled on arm64 [1] due to the lack of necessary > > > BBM(break-before-make) logic when changing page tables. > > > This set of patches fix this by adding necessary BBM sequence when > > > changing page table, and supporting vmemmap page fault handling to > > > fixup kernel address translation fault if vmemmap is concurrently accessed. > > I'm not keen on this approach. I'm not even sure it's safe. In the > > second patch, you take the init_mm.page_table_lock on the fault path but > > are we sure this is unlocked when the fault was taken? > I think this situation is impossible. In the implementation of the second > patch, when the page table is being corrupted > (the time window when a page fault may occur), vmemmap_update_pte() already > holds the init_mm.page_table_lock, > and unlock it until page table update is done.Another thread could not hold > the init_mm.page_table_lock and > also trigger a page fault at the same time. > If I have missed any points in my thinking, please correct me. Thank you. It still strikes me as incredibly fragile to handle the fault and trying to reason about all the users of 'struct page' is impossible. For example, can the fault happen from irq context? If we want to optimise the vmemmap mapping for arm64, I think we need to consider approaches which avoid the possibility of the fault altogether. It's more complicated to implement, but I think it would be a lot more robust. Andrew -- please can you drop these from -next? Thanks, Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel