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=-11.8 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 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 7F209C3A5A9 for ; Mon, 4 May 2020 07:13:20 +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 5346E21582 for ; Mon, 4 May 2020 07:13:20 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="eo3osV2A"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="PN6OVx5J" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5346E21582 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linuxfoundation.org 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-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject: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=uPnMLAMvflNXG4f2C2pDJWCWpV/qBsi8wXkOYMWsg7U=; b=eo3osV2Aebrfq8 OWUSQq02td5GAEW5N8Cn9tZalftUeYxr8DPTgHgCpFuQAhfDZ+TkahP8IHxaXEa70Ochqm3eW2qDg vIbFxdYBbE+ulutWgZ7qw93jqJ2JDSi7G1MFrIPfR/qpstkiWnWKVrtVmpRLDNCt016SbCyAR0kAY ycceMg9qKUDTJuVOcwWG58czTVEz1MZRpgTAXBAPsyyQhrXVgyxobKPpm+OqPJOGAjjD1boTdOtk4 /u/MnGQM+QKk8dr/V/AM+ksUMGbQ7IJHhkFkbwm1b3TC01C8SYbALCQKS+1r8m07bINhLXYcrs1dZ mfENZ/jA9gIfpKo3pFIA==; 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 1jVVHv-0002y3-D1; Mon, 04 May 2020 07:13:15 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1jVVHr-0002xJ-8T for linux-arm-kernel@lists.infradead.org; Mon, 04 May 2020 07:13:12 +0000 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 1CA5420757; Mon, 4 May 2020 07:13:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588576390; bh=XfFhhStBycJzV0puy65G2AGQGcJw71aLuImYtkVyKy0=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=PN6OVx5JB5/9SQpEja8hYrfZezsED5+zQGTFoXQ1/Tyk+8+nqB/XuGG0UuKkQweP+ FVlGCGy6RsuefwhtdM25LkXiPLAWeD78PCEqUKTZLBzzLkp84ji3V3DmIXA18j3RnO VnbSPAV01ET9XxFSbqCTDJ+NdEbt/8NTdzh/ly9s= Date: Mon, 4 May 2020 09:13:06 +0200 From: Greg KH To: Jeremy Linton Subject: Re: [PATCH] usb: usbfs: correct kernel->user page attribute mismatch Message-ID: <20200504071306.GA831956@kroah.com> References: <20200430211922.929165-1-jeremy.linton@arm.com> <20200501070500.GA887524@kroah.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200504_001311_338182_1F95CEF9 X-CRM114-Status: GOOD ( 39.26 ) 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-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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? thanks, greg k-h _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel