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=-7.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,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 A0AFBC432BE for ; Wed, 25 Aug 2021 10:59:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 85A1561212 for ; Wed, 25 Aug 2021 10:59:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240305AbhHYK7p (ORCPT ); Wed, 25 Aug 2021 06:59:45 -0400 Received: from foss.arm.com ([217.140.110.172]:48838 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240191AbhHYK7o (ORCPT ); Wed, 25 Aug 2021 06:59:44 -0400 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 8415C31B; Wed, 25 Aug 2021 03:58:58 -0700 (PDT) Received: from [10.57.15.112] (unknown [10.57.15.112]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id D502F3F766; Wed, 25 Aug 2021 03:58:56 -0700 (PDT) Subject: Re: [BUG 5.14] arm64/mm: dma memory mapping fails (in some cases) To: David Hildenbrand , Catalin Marinas Cc: Mike Rapoport , Alex Bee , Will Deacon , Andrew Morton , Anshuman Khandual , Linux Kernel Mailing List , linux-mm@kvack.org, Linux ARM , Christoph Hellwig References: <20210824173741.GC623@arm.com> <0908ce39-7e30-91fa-68ef-11620f9596ae@arm.com> <60a11eba-2910-3b5f-ef96-97d4556c1596@redhat.com> <20210825102044.GA3420@arm.com> From: Robin Murphy Message-ID: Date: Wed, 25 Aug 2021 11:58:51 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021-08-25 11:38, David Hildenbrand wrote: > On 25.08.21 12:20, Catalin Marinas wrote: >> + hch >> >> On Tue, Aug 24, 2021 at 08:59:22PM +0200, David Hildenbrand wrote: >>> On 24.08.21 20:46, Robin Murphy wrote: >>>> On 2021-08-24 19:28, Mike Rapoport wrote: >>>>> On Tue, Aug 24, 2021 at 06:37:41PM +0100, Catalin Marinas wrote: >>>>>> On Tue, Aug 24, 2021 at 03:40:47PM +0200, Alex Bee wrote: >>>>>>> it seems there is a regression in arm64 memory mapping in 5.14, >>>>>>> since it >>>>>>> fails on Rockchip RK3328 when the pl330 dmac tries to map with: >>>>>>> >>>>>>>   ------------[ cut here ]------------ >>>>>>>   WARNING: CPU: 2 PID: 373 at kernel/dma/mapping.c:235 >>>>>>> dma_map_resource+0x68/0xc0 >>>>>>>   Modules linked in: spi_rockchip(+) fuse >>>>>>>   CPU: 2 PID: 373 Comm: systemd-udevd Not tainted 5.14.0-rc7 #1 >>>>>>>   Hardware name: Pine64 Rock64 (DT) >>>>>>>   pstate: 80000005 (Nzcv daif -PAN -UAO -TCO BTYPE=--) >>>>>>>   pc : dma_map_resource+0x68/0xc0 >>>>>>>   lr : pl330_prep_slave_fifo+0x78/0xd0 >>>>>>>   sp : ffff800012102ae0 >>>>>>>   x29: ffff800012102ae0 x28: ffff000005c94800 x27: 0000000000000000 >>>>>>>   x26: ffff000000566bd0 x25: 0000000000000001 x24: 0000000000000001 >>>>>>>   x23: 0000000000000002 x22: ffff000000628c00 x21: 0000000000000001 >>>>>>>   x20: ffff000000566bd0 x19: 0000000000000001 x18: 0000000000000000 >>>>>>>   x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000000 >>>>>>>   x14: 0000000000000277 x13: 0000000000000001 x12: 0000000000000000 >>>>>>>   x11: 0000000000000001 x10: 00000000000008e0 x9 : ffff800012102a80 >>>>>>>   x8 : ffff000000d14b80 x7 : ffff0000fe7b12f0 x6 : ffff0000fe7b1100 >>>>>>>   x5 : fffffc000000000f x4 : 0000000000000000 x3 : 0000000000000001 >>>>>>>   x2 : 0000000000000001 x1 : 00000000ff190800 x0 : ffff000000628c00 >>>>>>>   Call trace: >>>>>>>     dma_map_resource+0x68/0xc0 >>>>>>>     pl330_prep_slave_sg+0x58/0x220 >>>>>>>     rockchip_spi_prepare_dma+0xd8/0x2c0 [spi_rockchip] >>>>>>>     rockchip_spi_transfer_one+0x294/0x3d8 [spi_rockchip] >>>>>> [...] >>>>>>> Note: This does not relate to the spi driver - when disabling >>>>>>> this device in >>>>>>> the device tree it fails for any other (i2s, for instance) which >>>>>>> uses dma. >>>>>>> Commenting out the failing check at [1], however, helps and the >>>>>>> mapping >>>>>>> works again. >>>>> >>>>>> Do you know which address dma_map_resource() is trying to map (maybe >>>>>> add some printk())? It's not supposed to map RAM, hence the warning. >>>>>> Random guess, the address is 0xff190800 (based on the x1 above but >>>>>> the >>>>>> regs might as well be mangled). >>>>> >>>>> 0xff190800 will cause this warning for sure. It has a memory map, >>>>> but it is >>>>> not RAM so old version of pfn_valid() would return 0 and the new one >>>>> returns 1. >>>> >>>> How does that happen, though? It's not a memory address, and it's not >>>> even within the bounds of anywhere there should or could be memory. >>>> This >>>> SoC has a simple memory map - everything from 0 to 0xfeffffff goes to >>>> the DRAM controller (which may not all be populated, and may have >>>> pieces >>>> carved out by secure firmware), while 0xff000000-0xffffffff is MMIO. >>>> Why >>>> do we have pages (or at least the assumption of pages) for somewhere >>>> which by all rights should not have them? >>> >>> Simple: we allocate the vmemmap for whole sections (e.g., 128 MiB) to >>> avoid >>> any such hacks. If there is a memory hole, it gets a memmap as well. Urgh, apologies for being slow. This case isn't a memory hole as such, but I failed to consider the *ends* of memory not being section-aligned and leading to an overlap anyway. >>> Tricking pfn_valid() into returning "false" where we actually have a >>> memmap >>> only makes it look like there is no memmap; but there is one, and >>> it's PG_reserved. >> >> 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) > > Would you expect to have a direct map for memory holes and similar (IOW, > !System RAM)? Probably - we can have no-map regions for firmware-reserved RAM which I believe end up as PG_reserved if they're small enough, for the same reasoning as this case. >>>>>> Either pfn_valid() gets confused in 5.14 or something is wrong >>>>>> with the >>>>>> DT. I have a suspicion it's the former since reverting the above >>>>>> commit >>>>>> makes it disappear. >>>>> >>>>> I think pfn_valid() actually behaves as expected but the caller is >>>>> wrong >>>>> because pfn_valid != RAM (this applies btw to !arm64 as well). >>>>> >>>>>     /* Don't allow RAM to be mapped */ >>>>>     if (WARN_ON_ONCE(pfn_valid(PHYS_PFN(phys_addr)))) >>>>>         return DMA_MAPPING_ERROR; >>>>> >>>>> Alex, can you please try this patch: >>>> >>>> That will certainly paper over the issue, but it's avoiding the >>>> question >>>> of what went wrong with the memory map in the first place. The comment >>>> is indeed a bit inaccurate, but ultimately dma_map_resource() exists >>>> for >>>> addresses that would be wrong to pass to dma_map_page(), so I believe >>>> pfn_valid() is still the correct check. >>> >>> If we want to check for RAM, pfn_valid() would be wrong. If we want >>> to check >>> for "is there a memmap, for whatever lives or does not live there", >>> pfn_valid() is the right check. >> >> So what should the DMA code use instead? Last time we needed something >> similar, the recommendation was to use pfn_to_online_page(). Mike is >> suggesting memblock_is_memory(). > > We use pfn_to_online_page() when we want to know if it's system RAM and > that the memmap actually contains something sane (-> memmap content has > a well defined state). > > You can have offline memory blocks where pfn_to_online_page() would > return "false", memblock_is_memory() would return "true". IOW, there is > a memmap, it's System RAM, but the memmap is stale and not trustworthy. That's fine - offline memory is doubly-invalid to map as an MMIO resource :) > If you want to make sure no System RAM (online/offline/...) will get > mapped, memblock_is_memory() should be the right thing to use. I recall > that x86 traverse the resource tree instead to exclude system ram > regions similarly. I'm thinking that "pfn_valid(pfn) && !PageReserved(pfn_to_page(pfn))" might be the closest thing to what I'd like to express - does that seem sensible at all? The one thing I'm not quite sure about is the interaction with P2P mappings of ZONE_DEVICE, but that's also true of the previous behaviour, and I'm not aware that the usage model has been fully nailed down yet, so I suspect we have some wiggle room. At worst, false negatives in certain situations wouldn't be the end of the world, since this is merely a sanity check for something which is expected to be a no-op the vast majority of the time, so being unobtrusive is more important than being exhaustive. Thanks, Robin. >> Given how later we are in the -rc cycle, I suggest we revert Anshuman's >> commit 16c9afc77660 ("arm64/mm: drop HAVE_ARCH_PFN_VALID") and try to >> assess the implications in 5.15 (the patch doesn't seem to have the >> arm64 maintainers' ack anyway ;)). >