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 X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 93BFBC433DB for ; Fri, 5 Feb 2021 10:34:27 +0000 (UTC) Received: from whitealder.osuosl.org (smtp1.osuosl.org [140.211.166.138]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id D065164F46 for ; Fri, 5 Feb 2021 10:34:26 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D065164F46 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lst.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=iommu-bounces@lists.linux-foundation.org Received: from localhost (localhost [127.0.0.1]) by whitealder.osuosl.org (Postfix) with ESMTP id 8AF7787205; Fri, 5 Feb 2021 10:34:26 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from whitealder.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id yM4nFabYt5J5; Fri, 5 Feb 2021 10:34:25 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [140.211.9.56]) by whitealder.osuosl.org (Postfix) with ESMTP id C659E86DCC; Fri, 5 Feb 2021 10:34:25 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id B63B0C0174; Fri, 5 Feb 2021 10:34:25 +0000 (UTC) Received: from whitealder.osuosl.org (smtp1.osuosl.org [140.211.166.138]) by lists.linuxfoundation.org (Postfix) with ESMTP id 3F877C013A for ; Fri, 5 Feb 2021 10:34:25 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by whitealder.osuosl.org (Postfix) with ESMTP id 2D9DF86DCC for ; Fri, 5 Feb 2021 10:34:25 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from whitealder.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id xrtTAg1idCps for ; Fri, 5 Feb 2021 10:34:24 +0000 (UTC) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from verein.lst.de (verein.lst.de [213.95.11.211]) by whitealder.osuosl.org (Postfix) with ESMTPS id D8C37871F9 for ; Fri, 5 Feb 2021 10:34:23 +0000 (UTC) Received: by verein.lst.de (Postfix, from userid 2407) id 53C6A68AFE; Fri, 5 Feb 2021 11:34:18 +0100 (CET) Date: Fri, 5 Feb 2021 11:34:17 +0100 From: Christoph Hellwig To: Robin Murphy Subject: Re: [PATCH 7/8] swiotlb: respect min_align_mask Message-ID: <20210205103417.GA6694@lst.de> References: <20210204193035.2606838-1-hch@lst.de> <20210204193035.2606838-8-hch@lst.de> <2e51481c-1591-034c-3476-1a1f8891506a@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <2e51481c-1591-034c-3476-1a1f8891506a@arm.com> User-Agent: Mutt/1.5.17 (2007-11-01) Cc: saravanak@google.com, konrad.wilk@oracle.com, marcorr@google.com, gregkh@linuxfoundation.org, linux-nvme@lists.infradead.org, kbusch@kernel.org, iommu@lists.linux-foundation.org, Christoph Hellwig , jxgao@google.com X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" On Thu, Feb 04, 2021 at 11:13:45PM +0000, Robin Murphy wrote: >> + */ >> +static unsigned int swiotlb_align_offset(struct device *dev, u64 addr) >> +{ >> + unsigned min_align_mask = dma_get_min_align_mask(dev); >> + >> + if (!min_align_mask) >> + return 0; > > I doubt that's beneficial - even if the compiler can convert it into a > csel, it'll then be doing unnecessary work to throw away a > cheaply-calculated 0 in favour of hard-coded 0 in the one case it matters True, I'll drop the checks. > ;) > >> + return addr & min_align_mask & ((1 << IO_TLB_SHIFT) - 1); > > (BTW, for readability throughout, "#define IO_TLB_SIZE (1 << IO_TLB_SHIFT)" > sure wouldn't go amiss...) I actually had a patch doing just that, but as it is the only patch touching swiotlb.h it caused endless rebuilds for me, so I dropped it as it only had a few uses anyway. But I've added it back. >> - if (alloc_size >= PAGE_SIZE) >> + if (min_align_mask) >> + stride = (min_align_mask + 1) >> IO_TLB_SHIFT; > > So this can't underflow because "min_align_mask" is actually just the > high-order bits representing the number of iotlb slots needed to meet the > requirement, right? (It took a good 5 minutes to realise this wasn't doing > what I initially thought it did...) Yes. > In that case, a) could the local var be called something like > iotlb_align_mask to clarify that it's *not* just a copy of the device's > min_align_mask, Ok. > and b) maybe just have an unconditional initialisation that > works either way: > > stride = (min_align_mask >> IO_TLB_SHIFT) + 1; Sure. > In fact with that, I think could just mask orig_addr with ~IO_TLB_SIZE in > the call to check_alignment() below, or shift everything down by > IO_TLB_SHIFT in check_alignment() itself, instead of mangling > min_align_mask at all (I'm assuming we do need to ignore the low-order bits > of orig_addr at this point). Yes, we do need to ignore the low bits as they won't ever be set in tlb_dma_addr. Not sure the shift helps as we need to mask first. I ended up killing check_alignment entirely, in favor of a new slot_addr helper that calculates the address based off the base and index and which can be used in a few other places as this one. _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu