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=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS autolearn=ham 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 06F59C43381 for ; Mon, 4 Mar 2019 23:56:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CF459206B6 for ; Mon, 4 Mar 2019 23:56:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726793AbfCDX4n (ORCPT ); Mon, 4 Mar 2019 18:56:43 -0500 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:41878 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726066AbfCDX4m (ORCPT ); Mon, 4 Mar 2019 18:56:42 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id D31D11596; Mon, 4 Mar 2019 15:56:41 -0800 (PST) Received: from [192.168.1.123] (usa-sjc-mx-foss1.foss.arm.com [217.140.101.70]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 575163F706; Mon, 4 Mar 2019 15:56:38 -0800 (PST) Subject: Re: [PATCH] Revert "swiotlb: remove SWIOTLB_MAP_ERROR" To: Arnd Bergmann , Konrad Rzeszutek Wilk , Boris Ostrovsky , Juergen Gross , Christoph Hellwig , Marek Szyprowski Cc: Stefano Stabellini , Mike Rapoport , Andrew Morton , Joerg Roedel , xen-devel@lists.xenproject.org, iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org References: <20190304195951.1118807-1-arnd@arndb.de> From: Robin Murphy Message-ID: Date: Mon, 4 Mar 2019 23:56:31 +0000 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:60.0) Gecko/20100101 Thunderbird/60.5.2 MIME-Version: 1.0 In-Reply-To: <20190304195951.1118807-1-arnd@arndb.de> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Arnd, On 2019-03-04 7:59 pm, Arnd Bergmann wrote: > This reverts commit b907e20508d0 ("swiotlb: remove SWIOTLB_MAP_ERROR"), which > introduced an overflow warning in configurations that have a larger > dma_addr_t than phys_addr_t: > > In file included from include/linux/dma-direct.h:5, > from kernel/dma/swiotlb.c:23: > kernel/dma/swiotlb.c: In function 'swiotlb_tbl_map_single': > include/linux/dma-mapping.h:136:28: error: conversion from 'long long unsigned int' to 'phys_addr_t' {aka 'unsigned int'} changes value from '18446744073709551615' to '4294967295' [-Werror=overflow] > #define DMA_MAPPING_ERROR (~(dma_addr_t)0) > ^ > kernel/dma/swiotlb.c:544:9: note: in expansion of macro 'DMA_MAPPING_ERROR' > return DMA_MAPPING_ERROR; > > The configuration that caused this is on 32-bit ARM, where the DMA address > space depends on the enabled hardware platforms, while the physical > address space depends on the type of MMU chosen (classic vs LPAE). Are these real platforms, or random configs? Realistically I don't see a great deal of need to support DMA_ADDR_T_64BIT for non-LPAE. Particularly in this case since AFAIK the only selector of SWIOTLB on Arm is Xen, and that by definition is never going to be useful on non-LPAE hardware. Fair enough that we don't still don't want even randconfigs generating warnings, though. As long as this change doesn't let SWIOTLB_MAP_ERROR leak out to logic expecting DMA_MAP_ERROR - which does appear to be the case - and is also still OK for the opposite weirdness of PHYS_ADDR_T_64BIT && !DMA_ADDR_T_64BIT, then I think it's reasonable. Robin. > I tried a couple of alternative approaches, but the previous version > seems as good as any other, so I went back to that. > > Fixes: b907e20508d0 ("swiotlb: remove SWIOTLB_MAP_ERROR") > Signed-off-by: Arnd Bergmann > --- > drivers/xen/swiotlb-xen.c | 4 ++-- > include/linux/swiotlb.h | 3 +++ > kernel/dma/swiotlb.c | 4 ++-- > 3 files changed, 7 insertions(+), 4 deletions(-) > > diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c > index 877baf2a94f4..57a98279bf4f 100644 > --- a/drivers/xen/swiotlb-xen.c > +++ b/drivers/xen/swiotlb-xen.c > @@ -406,7 +406,7 @@ static dma_addr_t xen_swiotlb_map_page(struct device *dev, struct page *page, > > map = swiotlb_tbl_map_single(dev, start_dma_addr, phys, size, dir, > attrs); > - if (map == DMA_MAPPING_ERROR) > + if (map == SWIOTLB_MAP_ERROR) > return DMA_MAPPING_ERROR; > > dev_addr = xen_phys_to_bus(map); > @@ -557,7 +557,7 @@ xen_swiotlb_map_sg_attrs(struct device *hwdev, struct scatterlist *sgl, > sg_phys(sg), > sg->length, > dir, attrs); > - if (map == DMA_MAPPING_ERROR) { > + if (map == SWIOTLB_MAP_ERROR) { > dev_warn(hwdev, "swiotlb buffer is full\n"); > /* Don't panic here, we expect map_sg users > to do proper error handling. */ > diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h > index 361f62bb4a8e..a65a36551f58 100644 > --- a/include/linux/swiotlb.h > +++ b/include/linux/swiotlb.h > @@ -44,6 +44,9 @@ enum dma_sync_target { > SYNC_FOR_DEVICE = 1, > }; > > +/* define the last possible byte of physical address space as a mapping error */ > +#define SWIOTLB_MAP_ERROR (~(phys_addr_t)0x0) > + > extern phys_addr_t swiotlb_tbl_map_single(struct device *hwdev, > dma_addr_t tbl_dma_addr, > phys_addr_t phys, size_t size, > diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c > index 12059b78b631..922880b84387 100644 > --- a/kernel/dma/swiotlb.c > +++ b/kernel/dma/swiotlb.c > @@ -541,7 +541,7 @@ phys_addr_t swiotlb_tbl_map_single(struct device *hwdev, > spin_unlock_irqrestore(&io_tlb_lock, flags); > if (!(attrs & DMA_ATTR_NO_WARN) && printk_ratelimit()) > dev_warn(hwdev, "swiotlb buffer is full (sz: %zd bytes)\n", size); > - return DMA_MAPPING_ERROR; > + return SWIOTLB_MAP_ERROR; > found: > io_tlb_used += nslots; > spin_unlock_irqrestore(&io_tlb_lock, flags); > @@ -659,7 +659,7 @@ bool swiotlb_map(struct device *dev, phys_addr_t *phys, dma_addr_t *dma_addr, > /* Oh well, have to allocate and map a bounce buffer. */ > *phys = swiotlb_tbl_map_single(dev, __phys_to_dma(dev, io_tlb_start), > *phys, size, dir, attrs); > - if (*phys == DMA_MAPPING_ERROR) > + if (*phys == SWIOTLB_MAP_ERROR) > return false; > > /* Ensure that the address returned is DMA'ble */ >