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Date: Thu, 15 Aug 2024 21:53:02 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Huang Ying <ying.huang@intel.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
 linux-cxl@vger.kernel.org, Dan Williams <dan.j.williams@intel.com>,
 Davidlohr Bueso <dave@stgolabs.net>, Jonathan Cameron
 <jonathan.cameron@huawei.com>, Dave Jiang <dave.jiang@intel.com>, Alison
 Schofield <alison.schofield@intel.com>, Vishal Verma
 <vishal.l.verma@intel.com>, Ira Weiny <ira.weiny@intel.com>, Alistair
 Popple <apopple@nvidia.com>, Andy Shevchenko
 <andriy.shevchenko@linux.intel.com>, Bjorn Helgaas <bhelgaas@google.com>,
 Baoquan He <bhe@redhat.com>
Subject: Re: [PATCH] Resource: fix region_intersects() for CXL memory
Message-Id: <20240815215302.5ed29b99e94a48aea49269ce@linux-foundation.org>
In-Reply-To: <20240816020723.771196-1-ying.huang@intel.com>
References: <20240816020723.771196-1-ying.huang@intel.com>
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On Fri, 16 Aug 2024 10:07:23 +0800 Huang Ying <ying.huang@intel.com> 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
> ...
>

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")?