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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, 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 BED49C4320A for ; Wed, 25 Aug 2021 17:15:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A1C8060EE5 for ; Wed, 25 Aug 2021 17:15:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242232AbhHYRQo (ORCPT ); Wed, 25 Aug 2021 13:16:44 -0400 Received: from mail.kernel.org ([198.145.29.99]:49622 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232493AbhHYRQn (ORCPT ); Wed, 25 Aug 2021 13:16:43 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id AD50F61076; Wed, 25 Aug 2021 17:15:55 +0000 (UTC) Date: Wed, 25 Aug 2021 18:15:53 +0100 From: Catalin Marinas To: David Hildenbrand Cc: Robin Murphy , Mike Rapoport , Alex Bee , Will Deacon , Andrew Morton , Anshuman Khandual , Linux Kernel Mailing List , linux-mm@kvack.org, Linux ARM , Christoph Hellwig Subject: Re: [BUG 5.14] arm64/mm: dma memory mapping fails (in some cases) Message-ID: <20210825171552.GH3420@arm.com> References: <20210824173741.GC623@arm.com> <0908ce39-7e30-91fa-68ef-11620f9596ae@arm.com> <60a11eba-2910-3b5f-ef96-97d4556c1596@redhat.com> <20210825102044.GA3420@arm.com> <20210825105510.GB3420@arm.com> <547785ff-e02f-df28-7f9c-9ad4f5b3cc77@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <547785ff-e02f-df28-7f9c-9ad4f5b3cc77@redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Aug 25, 2021 at 01:12:37PM +0200, David Hildenbrand wrote: > On 25.08.21 12:55, Catalin Marinas wrote: > > On Wed, Aug 25, 2021 at 12:38:31PM +0200, David Hildenbrand wrote: > > > On 25.08.21 12:20, Catalin Marinas wrote: > > > > I can see the documentation for pfn_valid() does not claim anything more > > > > than the presence of an memmap entry. But I wonder whether the confusion > > > > is wider-spread than just the DMA code. At a quick grep, try_ram_remap() > > > > assumes __va() can be used on pfn_valid(), though I suspect it relies on > > > > the calling function to check that the resource was RAM. The arm64 > > > > kern_addr_valid() returns true based on pfn_valid() and kcore.c uses > > > > standard memcpy on it, which wouldn't work for I/O (should we change > > > > this check to pfn_is_map_memory() for arm64?). > > > > > > kern_addr_valid() checks that there is a direct map entry, and that the > > > mapped address has a valid mmap. (copied from x86-64) > > > > It checks that there is a va->pa mapping, not necessarily in the linear > > map as it walks the page tables. So for some I/O range that happens to > > be mapped but which was in close proximity to RAM so that pfn_valid() is > > true, kern_addr_valid() would return true. I don't thin that was the > > intention. > > > > > Would you expect to have a direct map for memory holes and similar (IOW, > > > !System RAM)? > > > > No, but we with the generic pfn_valid(), it may return true for mapped > > MMIO (with different attributes than the direct map). > > Ah, right. But can we actually run into that via kcore? > > kcore builds the RAM list via walk_system_ram_range(), IOW the resource > tree. And we end up calling kern_addr_valid() only on KCORE_RAM, > KCORE_VMEMMAP and KCORE_TEXT. It's probably fine but I'd rather do some check of the other call sites before attempting to move arm64 to the generic pfn_valid() again. -- Catalin