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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_MUTT 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 E8B91C31E44 for ; Fri, 14 Jun 2019 09:48:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BD6C921473 for ; Fri, 14 Jun 2019 09:48:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727249AbfFNJsF (ORCPT ); Fri, 14 Jun 2019 05:48:05 -0400 Received: from verein.lst.de ([213.95.11.211]:45593 "EHLO newverein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726900AbfFNJsE (ORCPT ); Fri, 14 Jun 2019 05:48:04 -0400 Received: by newverein.lst.de (Postfix, from userid 2407) id 1E342227A82; Fri, 14 Jun 2019 11:47:34 +0200 (CEST) Date: Fri, 14 Jun 2019 11:47:34 +0200 From: Christoph Hellwig To: Florian Fainelli Cc: linux-kernel@vger.kernel.org, bcm-kernel-feedback-list@broadcom.com, Christoph Hellwig , Marek Szyprowski , Robin Murphy , Konrad Rzeszutek Wilk , Andrew Lunn , Vivien Didelot , "David S. Miller" , "open list:DMA MAPPING HELPERS" , "open list:NETWORKING [GENERAL]" Subject: Re: [PATCH 2/2] swiotlb: Return consistent SWIOTLB segments/nr_tbl Message-ID: <20190614094734.GH17292@lst.de> References: <20190611175825.572-1-f.fainelli@gmail.com> <20190611175825.572-3-f.fainelli@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190611175825.572-3-f.fainelli@gmail.com> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Tue, Jun 11, 2019 at 10:58:25AM -0700, Florian Fainelli wrote: > With a specifically contrived memory layout where there is no physical > memory available to the kernel below the 4GB boundary, we will fail to > perform the initial swiotlb_init() call and set no_iotlb_memory to true. > > There are drivers out there that call into swiotlb_nr_tbl() to determine > whether they can use the SWIOTLB. With the right DMA_BIT_MASK() value > for these drivers (say 64-bit), they won't ever need to hit > swiotlb_tbl_map_single() so this can go unoticed and we would be > possibly lying about those drivers. > > Signed-off-by: Florian Fainelli > --- > kernel/dma/swiotlb.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c > index b2b5c5df273c..e906ef2e6315 100644 > --- a/kernel/dma/swiotlb.c > +++ b/kernel/dma/swiotlb.c > @@ -129,15 +129,17 @@ setup_io_tlb_npages(char *str) > } > early_param("swiotlb", setup_io_tlb_npages); > > +static bool no_iotlb_memory; > + > unsigned long swiotlb_nr_tbl(void) > { > - return io_tlb_nslabs; > + return unlikely(no_iotlb_memory) ? 0 : io_tlb_nslabs; > } > EXPORT_SYMBOL_GPL(swiotlb_nr_tbl); > > unsigned int swiotlb_max_segment(void) > { > - return max_segment; > + return unlikely(no_iotlb_memory) ? 0 : max_segment; I wouldn't bother with the unlikely here as anythign querying swiotlb details should pretty much be a slow path already. Otherwise looks good: Reviewed-by: Christoph Hellwig