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[149.14.88.26]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-607783dccbdsm7104469a12.54.2025.06.11.01.23.20 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 11 Jun 2025 01:23:21 -0700 (PDT) Message-ID: <52b746ae-82cc-428e-8e88-a05a6b738cd0@redhat.com> Date: Wed, 11 Jun 2025 10:23:20 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: Remove PFN_MAP, PFN_SPECIAL, PFN_SG_CHAIN and PFN_SG_LAST To: Marek Szyprowski , Alistair Popple Cc: linux-mm@kvack.org, akpm@linux-foundation.org, "linux-riscv@lists.infradead.org" , Christoph Hellwig , Jason Gunthorpe , gerald.schaefer@linux.ibm.com, dan.j.williams@intel.com, jgg@ziepe.ca, willy@infradead.org, linux-kernel@vger.kernel.org, nvdimm@lists.linux.dev, jhubbard@nvidia.com, zhang.lyra@gmail.com, debug@rivosinc.com, bjorn@kernel.org, balbirs@nvidia.com, lorenzo.stoakes@oracle.com, John@groves.net References: <20250604032145.463934-1-apopple@nvidia.com> <957c0d9d-2c37-4d5f-a8b8-8bf90cd0aedb@samsung.com> <1daeaf4e-5477-40cb-bca0-e4cd5ad8a224@samsung.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset="us-ascii"; Format="flowed" Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org On 11.06.25 10:03, Marek Szyprowski wrote: > On 11.06.2025 04:38, Alistair Popple wrote: >> On Tue, Jun 10, 2025 at 06:18:09PM +0200, Marek Szyprowski wrote: >>> On 04.06.2025 05:21, Alistair Popple wrote: >>>> The PFN_MAP flag is no longer used for anything, so remove it. >>>> The PFN_SG_CHAIN and PFN_SG_LAST flags never appear to have been >>>> used so also remove them. The last user of PFN_SPECIAL was removed >>>> by 653d7825c149 ("dcssblk: mark DAX broken, remove FS_DAX_LIMITED >>>> support"). >>>> >>>> Signed-off-by: Alistair Popple >>>> Acked-by: David Hildenbrand >>>> Reviewed-by: Christoph Hellwig >>>> Reviewed-by: Jason Gunthorpe >>>> Cc: gerald.schaefer@linux.ibm.com >>>> Cc: dan.j.williams@intel.com >>>> Cc: jgg@ziepe.ca >>>> Cc: willy@infradead.org >>>> Cc: david@redhat.com >>>> Cc: linux-kernel@vger.kernel.org >>>> Cc: nvdimm@lists.linux.dev >>>> Cc: jhubbard@nvidia.com >>>> Cc: hch@lst.de >>>> Cc: zhang.lyra@gmail.com >>>> Cc: debug@rivosinc.com >>>> Cc: bjorn@kernel.org >>>> Cc: balbirs@nvidia.com >>>> Cc: lorenzo.stoakes@oracle.com >>>> Cc: John@Groves.net >>>> >>>> --- >>>> >>>> Splitting this off from the rest of my series[1] as a separate clean-up >>>> for consideration for the v6.16 merge window as suggested by Christoph. >>>> >>>> [1] - https://lore.kernel.org/linux-mm/cover.541c2702181b7461b84f1a6967a3f0e823023fcc.1748500293.git-series.apopple@nvidia.com/ >>>> --- >>>> include/linux/pfn_t.h | 31 +++---------------------------- >>>> mm/memory.c | 2 -- >>>> tools/testing/nvdimm/test/iomap.c | 4 ---- >>>> 3 files changed, 3 insertions(+), 34 deletions(-) >>> This patch landed in today's linux-next as commit 28be5676b4a3 ("mm: >>> remove PFN_MAP, PFN_SPECIAL, PFN_SG_CHAIN and PFN_SG_LAST"). In my tests >>> I've noticed that it breaks operation of all RISC-V 64bit boards on my >>> test farm (VisionFive2, BananaPiF3 as well as QEMU's Virt machine). I've >>> isolated the changes responsible for this issue, see the inline comments >>> in the patch below. Here is an example of the issues observed in the >>> logs from those machines: >> Thanks for the report. I'm really confused by this because this change should >> just be removal of dead code - nothing sets any of the removed PFN_* flags >> AFAICT. >> >> I don't have access to any RISC-V hardwdare but you say this reproduces under >> qemu - what do you run on the system to cause the error? Is it just a simple >> boot and load a module or are you running selftests or something else? > > It fails a simple boot test. Here is a detailed instruction how to > reproduce this issue with the random Debian rootfs image found on the > internet (tested on Ubuntu 22.04, with next-20250610 > kernel source): riscv is one of the archs where pte_mkdevmap() will *not* set the pte as special. (I raised this recently in the original series, it's all a big mess) So, before this change here, pfn_t_devmap() would have returned "false" if only PFN_DEV was set, now it would return "true" if only PFN_DEV is set. Consequently, in insert_pfn() we would have done a pte_mkspecial(), now we do a pte_mkdevmap() -- again, which does not imply "special" on riscv. riscv selects CONFIG_ARCH_HAS_PTE_SPECIAL, so if !pte_special(), it's considered as normal. Would the following fix your issue? diff --git a/mm/memory.c b/mm/memory.c index 8eba595056fe3..0e972c3493692 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -589,6 +589,10 @@ struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr, { unsigned long pfn = pte_pfn(pte); + /* TODO: remove this crap and set pte_special() instead. */ + if (pte_devmap(pte)) + return NULL; + if (IS_ENABLED(CONFIG_ARCH_HAS_PTE_SPECIAL)) { if (likely(!pte_special(pte))) goto check_pfn; @@ -598,16 +602,6 @@ struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr, return NULL; if (is_zero_pfn(pfn)) return NULL; - if (pte_devmap(pte)) - /* - * NOTE: New users of ZONE_DEVICE will not set pte_devmap() - * and will have refcounts incremented on their struct pages - * when they are inserted into PTEs, thus they are safe to - * return here. Legacy ZONE_DEVICE pages that set pte_devmap() - * do not have refcounts. Example of legacy ZONE_DEVICE is - * MEMORY_DEVICE_FS_DAX type in pmem or virtio_fs drivers. - */ - return NULL; print_bad_pte(vma, addr, pte, NULL); return NULL; But, I would have thought the later patches in Alistairs series would sort that out (where we remove pte_devmap() ... ) -- Cheers, David / dhildenb _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv