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[2003:cb:c721:b900:4f34:b2b7:739d:a650]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-429ded7ead3sm72048675e9.47.2024.08.16.01.57.37 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 16 Aug 2024 01:57:38 -0700 (PDT) Message-ID: <192dcb60-e274-4b2c-a626-608bee4dbe65@redhat.com> Date: Fri, 16 Aug 2024 10:57:36 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] Resource: fix region_intersects() for CXL memory To: Dan Williams , Andrew Morton , Huang Ying Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-cxl@vger.kernel.org, Davidlohr Bueso , Jonathan Cameron , Dave Jiang , Alison Schofield , Vishal Verma , Ira Weiny , Alistair Popple , Andy Shevchenko , Bjorn Helgaas , Baoquan He References: <20240816020723.771196-1-ying.huang@intel.com> <20240815215302.5ed29b99e94a48aea49269ce@linux-foundation.org> <66bede74cb96f_1c18294ce@dwillia2-mobl3.amr.corp.intel.com.notmuch> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 16.08.24 07:07, Dan Williams wrote: > [ add David ] > > Andrew Morton wrote: >> On Fri, 16 Aug 2024 10:07:23 +0800 Huang Ying wrote: >> >>> On a system with CXL memory installed, the resource tree (/proc/iomem) >>> related to CXL memory looks like something as follows. >>> >>> 490000000-50fffffff : CXL Window 0 >>> 490000000-50fffffff : region0 >>> 490000000-50fffffff : dax0.0 >>> 490000000-50fffffff : System RAM (kmem) >>> >>> When the following command line is run to try writing some memory in >>> CXL memory range, >>> >>> $ dd if=data of=/dev/mem bs=1k seek=19136512 count=1 >>> dd: error writing '/dev/mem': Bad address >>> 1+0 records in >>> 0+0 records out >>> 0 bytes copied, 0.0283507 s, 0.0 kB/s >>> >>> the command fails as expected. However, the error code is wrong. It >>> should be "Operation not permitted" instead of "Bad address". And, >>> the following warning is reported in kernel log. >>> >>> ioremap on RAM at 0x0000000490000000 - 0x0000000490000fff >>> WARNING: CPU: 2 PID: 416 at arch/x86/mm/ioremap.c:216 __ioremap_caller.constprop.0+0x131/0x35d But we should definitely fix the warning. >>> ... >>> >> >> Presumably we want to fix earlier kernels? If so, are you able to >> identify a suitable Fixes: target? Possibly 974854ab0728 ("cxl/acpi: >> Track CXL resources in iomem_resource")? > > At least that commit, but I think this problem potentially goes back > farther to: > > c221c0b0308f device-dax: "Hotplug" persistent memory for use like normal RAM > > ...because that started the era of "System RAM" as a non-top-level > resource. > > David did a bunch of work to fix this back in: > > 97f61c8f44ec kernel/resource: make walk_system_ram_res() find all busy IORESOURCE_SYSTEM_RAM resources > > ..but the fallout in region_intersects() was missed. Sounds reasonable. For virtio-mem we set IORESOURCE_SYSTEM_RAM|IORESOURCE_EXCLUSIVE on our (highest) parent resource (to make any /dev/mem access attempts of that memory fail). So the problem is likely specific to other add_memory_driver_managed() users. I have a faint recollection that at some point we had code that would set IORESOURCE_SYSTEM_RAM on parent resources up the tree, but either my memory is wrong or that code was ripped out long ago. Fix idea is reasonable: check if anything in that range is IORESOURCE_SYSTEM_RAM. -- Cheers, David / dhildenb