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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id A30CBC761A6 for ; Wed, 5 Apr 2023 22:54:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231889AbjDEWyK (ORCPT ); Wed, 5 Apr 2023 18:54:10 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41962 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231245AbjDEWyJ (ORCPT ); Wed, 5 Apr 2023 18:54:09 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B6CD940DA; Wed, 5 Apr 2023 15:54:08 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 5DE3D64143; Wed, 5 Apr 2023 22:54:08 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 722A6C433EF; Wed, 5 Apr 2023 22:54:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1680735247; bh=y5XoOju2yBDL4YDibMiieXpA89mTn+Rteq91AiPxCaU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=LovyRg/EAV0o26rHWyr3wwdJKBIWeqs2RWTqBiuMA93Uopo6KQP/kuk5d1BnGrKHX eXiQmEFzna6WH31jznXOQEsuU8fCZaqbF53Fy9IDiBzVWVzNlq3Fcms5RC/AHMk3CM OAU4zbey8PXa+toYXE1InTyNADGV791ee94FuTsdJtQmtxfk26JoNlrEZbAnyuI7RM Tdnt072GBeEL29vP8V8lyr806zJWwdzwvcrm09fKje0OdHL52/Fkji9DdhPvGeeRQZ JSFgndGfwhFR5/2N8nLhm2oMnQAOUpmI5ryVtmOxxrkwIl3UfC3Gz24KpM4fDrDRV4 EANBOVoAcG1Tg== Date: Wed, 5 Apr 2023 22:54:06 +0000 From: Eric Biggers To: Dave Chinner Cc: "Darrick J. Wong" , Andrey Albershteyn , dchinner@redhat.com, hch@infradead.org, linux-xfs@vger.kernel.org, fsverity@lists.linux.dev, rpeterso@redhat.com, agruenba@redhat.com, xiang@kernel.org, chao@kernel.org, damien.lemoal@opensource.wdc.com, jth@kernel.org, linux-erofs@lists.ozlabs.org, linux-btrfs@vger.kernel.org, linux-ext4@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, cluster-devel@redhat.com Subject: Re: [PATCH v2 21/23] xfs: handle merkle tree block size != fs blocksize != PAGE_SIZE Message-ID: References: <20230404145319.2057051-1-aalbersh@redhat.com> <20230404145319.2057051-22-aalbersh@redhat.com> <20230404163602.GC109974@frogsfrogsfrogs> <20230405160221.he76fb5b45dud6du@aalbersh.remote.csb> <20230405163847.GG303486@frogsfrogsfrogs> <20230405222646.GR3223426@dread.disaster.area> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230405222646.GR3223426@dread.disaster.area> Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Thu, Apr 06, 2023 at 08:26:46AM +1000, Dave Chinner wrote: > > We could certainly think about moving to a design where fs/verity/ asks the > > filesystem to just *read* a Merkle tree block, without adding it to a cache, and > > then fs/verity/ implements the caching itself. That would require some large > > changes to each filesystem, though, unless we were to double-cache the Merkle > > tree blocks which would be inefficient. > > No, that's unnecessary. > > All we need if for fsverity to require filesystems to pass it byte > addressable data buffers that are externally reference counted. The > filesystem can take a page reference before mapping the page and > passing the kaddr to fsverity, then unmap and drop the reference > when the merkle tree walk is done as per Andrey's new drop callout. > > fsverity doesn't need to care what the buffer is made from, how it > is cached, what it's life cycle is, etc. The caching mechanism and > reference counting is entirely controlled by the filesystem callout > implementations, and fsverity only needs to deal with memory buffers > that are guaranteed to live for the entire walk of the merkle > tree.... Sure. Just a couple notes: First, fs/verity/ does still need to be able to tell whether the buffer is newly instantiated or not. Second, fs/verity/ uses the ahash API to do the hashing. ahash is a scatterlist-based API. Virtual addresses can still be used (see sg_set_buf()), but the memory cannot be vmalloc'ed memory, since virt_to_page() needs to work. Does XFS use vmalloc'ed memory for these buffers? BTW, converting fs/verity/ from ahash to shash is an option; I've really never been a fan of the scatterlist-based crypto APIs! The disadvantage of doing this, though, would be that it would remove support for all the hardware crypto drivers. That *might* actually be okay, as that approach to crypto acceleration has mostly fallen out of favor, in favor of CPU-based acceleration. But I do worry about e.g. someone coming out of the woodwork and saying they need to use fsverity on a low-powered ARM board that has a crypto accelerator like CAAM, and they MUST use their crypto accelerator to get acceptable performance. - Eric