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=-13.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 417ABC3A5A9 for ; Mon, 4 May 2020 13:21:45 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id 0F3EE2073B for ; Mon, 4 May 2020 13:21:45 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="CuZGA7JD" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0F3EE2073B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender:Content-Type: Content-Transfer-Encoding:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date:Message-ID:From: References:To:Subject:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=KS8W9+09f8L8yP2XaDCm3i772l0B2sqR1XZjiFC+Fpo=; b=CuZGA7JDZV+Wfk+BP4VnteDyk kRbrpwQ4agTcqI1wtA56ScRaWwU5YoUdjeForQySdz55pCeFkBQLxuaALy9nqEiiLQ426zeQrm8s1 qSEMRD80TdyF8o37bnEY3czM03IFW7RtlXM4M2hf21MVMneyZSh+ivdHFP1XlpED/LE6/8QEPcezG 5Qq8rjKsIqxUSa9SYyR5y8DNfbhlASwMcGlWvfTsi3KkqkqSqC147OlGoE5Bsep2hV5EkaHuYXOn2 GRPHFwC/uSvwaWk27W62vKt8GXpeX5D3T5CdDfD15MJ9+u3d+EUzw9uMN9tpcknxp+gWURSSJwxp8 Q2apk9OBA==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jVb2S-000554-Vx; Mon, 04 May 2020 13:21:40 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jVb2Q-00054c-A1 for linux-arm-kernel@lists.infradead.org; Mon, 04 May 2020 13:21:40 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id B3A691FB; Mon, 4 May 2020 06:21:35 -0700 (PDT) Received: from [192.168.122.166] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 76A493F71F; Mon, 4 May 2020 06:21:35 -0700 (PDT) Subject: Re: [PATCH] usb: usbfs: correct kernel->user page attribute mismatch To: Greg KH References: <20200430211922.929165-1-jeremy.linton@arm.com> <20200501070500.GA887524@kroah.com> <20200504071306.GA831956@kroah.com> From: Jeremy Linton Message-ID: Date: Mon, 4 May 2020 08:21:31 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <20200504071306.GA831956@kroah.com> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200504_062138_435314_EECFB3D2 X-CRM114-Status: GOOD ( 28.07 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: git@thegavinli.com, linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org, jarkko.sakkinen@linux.intel.com, stern@rowland.harvard.edu, linux-arm-kernel@lists.infradead.org Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi, On 5/4/20 2:13 AM, Greg KH wrote: > On Fri, May 01, 2020 at 10:47:22AM -0500, Jeremy Linton wrote: >> Hi, >> >> Thanks for taking a look at this. >> >> On 5/1/20 2:05 AM, Greg KH wrote: >>> On Thu, Apr 30, 2020 at 04:19:22PM -0500, Jeremy Linton wrote: >>>> On arm64, and possibly other architectures, requesting >>>> IO coherent memory may return Normal-NC if the underlying >>>> hardware isn't coherent. If these pages are then >>>> remapped into userspace as Normal, that defeats the >>>> purpose of getting Normal-NC, as well as resulting in >>>> mappings with differing cache attributes. >>> >>> What is "Normal-NC"? >> >> A non-cacheable attribute on arm64 pages. I think Mark R & Marc Z elaborated >> while I was asleep (thanks!). >> . >> >> >>> >>>> In particular this happens with libusb, when it attempts >>>> to create zero-copy buffers as is used by rtl-sdr, and >>> >>> What is "rtl-sdr" >> >> Its the realtek software defined radio (SDR), a really inexpensive TV dongle >> that was discovered could be used as a general purpose SDR a decade or so >> ago. In particular, this project >> https://github.com/osmocom/rtl-sdr/ >> which is packaged by fedora/etc. >> >>> >>>> maybe other applications. The result is usually >>>> application death. >>> >>> So is this a new problem? Old problem? Old problem only showing up on >>> future devices? On current devices? I need a hint here as to know if >>> this is a bugfix or just work to make future devices work properly. >> >> This has been a problem on arm devices without IO coherent USB apparently >> for years. The rtl-sdr project itself has a disable zero-copy mode that >> people have been using on rpi/etc specific builds. Fedora OTOH, is building >> it with the same flags on x86 & arm64 which means that people report >> problems. This happened a few days ago (on a pinebook), and I duplicated it >> on an NXP platform just running the `rtl_test` artifact with a nooelec from >> my junk box. Guessing that it was a page mismatch I went looking for that, >> rather than disabling the zero copy since punishing arm machine that have IO >> coherent USB adapters for the sins of these low end devices isn't ideal. I >> found this, and this patch allows the rtl_test app to run without issues on >> my NXP/solidrun. >> >> Plus, given that its actually a kernel/libusb problem its likely there are >> other applications having similar problems. >> >>> >>>> >>>> If dma_mmap_attr() is used instead of remap_pfn_range, >>>> the page cache/etc attributes can be matched between the >>>> kernel and userspace. >>>> >>>> Signed-off-by: Jeremy Linton >>>> --- >>>> drivers/usb/core/devio.c | 5 ++--- >>>> 1 file changed, 2 insertions(+), 3 deletions(-) >>>> >>>> diff --git a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c >>>> index 6833c918abce..1e7458dd6e5d 100644 >>>> --- a/drivers/usb/core/devio.c >>>> +++ b/drivers/usb/core/devio.c >>>> @@ -217,6 +217,7 @@ static int usbdev_mmap(struct file *file, struct vm_area_struct *vma) >>>> { >>>> struct usb_memory *usbm = NULL; >>>> struct usb_dev_state *ps = file->private_data; >>>> + struct usb_hcd *hcd = bus_to_hcd(ps->dev->bus); >>>> size_t size = vma->vm_end - vma->vm_start; >>>> void *mem; >>>> unsigned long flags; >>>> @@ -250,9 +251,7 @@ static int usbdev_mmap(struct file *file, struct vm_area_struct *vma) >>>> usbm->vma_use_count = 1; >>>> INIT_LIST_HEAD(&usbm->memlist); >>>> - if (remap_pfn_range(vma, vma->vm_start, >>>> - virt_to_phys(usbm->mem) >> PAGE_SHIFT, >>>> - size, vma->vm_page_prot) < 0) { >>>> + if (dma_mmap_attrs(hcd->self.sysdev, vma, mem, dma_handle, size, 0)) { >>> >>> Given that this code has not changed since 2016, how has no one noticed >>> this issue before? >> They have there are a lot of reports of sdr failures, but the general use >> case is rare? >> >>> >>> And have you tested this change out on other systems (i.e. x86) to >>> ensure that this still works properly? >> >> Yes and no, I did some basic libusb tests on an x86 machine, but its a bit >> tricky at the moment for me to get the rtl plugged into a x86 test machine. >> (its a work in progress). >> >> >>> >>> And why isn't this call used more by drivers if this is a real issue? >> The particulars of asking for iocoherent memory and then mapping it to >> userspace is rarer than just asking for kmalloc()/remap() and then >> performing the dma ops? >> >> Then there are all the softer issues around arm64 testing/availability and >> vendors carrying "fixes" for particular issues (like rtl-sdr disabling zero >> copy). >> >>> And will this cause issues with how the userspace mapping is handled as >>> now we rely on userspace to do things differently? Or am I reading the >>> dma_mmap_attrs() documentation wrong? >> I don't think userspace is doing anything differently here, and AFAIK, on >> systems with IO coherent adapters this ends up with the same page mapping as >> just doing the remap_pfn_rage() with the same attributes as before. I've >> looked at dma_map_attrs() a bit, but i'm also trusting it does what it says >> on the tin. >> >> >> Thanks again for looking at this. > > Ok, can I get a lot better written changelog text for this patch based > on this thread, so that it makes more sense when we merge this patch? Yes, sure. I also plan on changing it to dma_mmap_coherent() which is the same as the dma_mmap_attrs() with the attrs as above. I will re-post later this afternoon. Thanks, _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel