Re: [PATCH] cxl_test: Limit location for fake CFMWS to mappable range

[Alison Schofield <alison.schofield@intel.com>]

On Tue, May 27, 2025 at 04:34:51PM +0100, Jonathan Cameron wrote:
> Some architectures (e.g. arm64) only support memory hotplug operations on
> a restricted set of physical addresses. This applies even when we are
> faking some CXL fixed memory windows for the purposes of cxl_test.
> That range can be queried with mhp_get_pluggable_range(true). Use the
> minimum of that the top of that range and iomem_resource.end to establish
> the 64GiB region used by cxl_test.
> 
> From thread #2 which was related to the issue in #1.
> 
> Link: https://lore.kernel.org/linux-cxl/20250522145622.00002633@huawei.com/ #2
> Reported-by: Itaru Kitayama <itaru.kitayama@linux.dev>
> Closes: https://github.com/pmem/ndctl/issues/278 #1
> Reviewed-by: Dan Williams <dan.j.williams@intel.com>
> Tested-by: Itaru Kitayama <itaru.kitayama@fujitsu.com <mailto:itaru.kitayama@fujitsu.com>
> Tested-by: Marc Herbert <marc.herbert@linux.intel.com>
> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> 
> ---
> I haven't given this a fixes tag because it never worked on arm64.
> So it isn't a regression fix, and I'm not sure we want to back port this
> which a fixes tag might well trigger.  If people want one shout and I'll
> try and figure out what is appropriate.
> ---
>  tools/testing/cxl/test/cxl.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/testing/cxl/test/cxl.c b/tools/testing/cxl/test/cxl.c
> index 8a5815ca870d..6a25cca5636f 100644
> --- a/tools/testing/cxl/test/cxl.c
> +++ b/tools/testing/cxl/test/cxl.c
> @@ -2,6 +2,7 @@
>  // Copyright(c) 2021 Intel Corporation. All rights reserved.
>  
>  #include <linux/platform_device.h>
> +#include <linux/memory_hotplug.h>
>  #include <linux/genalloc.h>
>  #include <linux/module.h>
>  #include <linux/mutex.h>
> @@ -1328,6 +1329,7 @@ static int cxl_mem_init(void)
>  static __init int cxl_test_init(void)
>  {
>  	int rc, i;
> +	struct range mappable;
>  
>  	cxl_acpi_test();
>  	cxl_core_test();
> @@ -1342,8 +1344,11 @@ static __init int cxl_test_init(void)
>  		rc = -ENOMEM;
>  		goto err_gen_pool_create;
>  	}
> +	mappable = mhp_get_pluggable_range(true);

mhp_get_pluaggable_range() is only defined w CONFIG_MEMORY_HOTPLUG

This to tools/testing/cxl/config_check.c works for me:
+       BUILD_BUG_ON(!IS_ENABLED(CONFIG_MEMORY_HOTPLUG));


>  
> -	rc = gen_pool_add(cxl_mock_pool, iomem_resource.end + 1 - SZ_64G,
> +	rc = gen_pool_add(cxl_mock_pool,
> +			  min(iomem_resource.end + 1 - SZ_64G,
> +			      mappable.end + 1 - SZ_64G),
>  			  SZ_64G, NUMA_NO_NODE);
>  	if (rc)
>  		goto err_gen_pool_add;
> -- 
> 2.43.0
>