Re: [PATCH] tools/testing/cxl: Align mock CFMWS to PMD_SIZE for ARM64 64K pages

[Dave Jiang]

On 5/19/26 4:35 PM, Richard Cheng wrote:
> cxl_test allocate synthetic CFMWS HPA windows out of a gen_pool and asks
> the allocator for SZ_256M alignment. It has been sufficient on x86 with
> 4k pages, arm64 with 4k pages since their PMD_SIZE are 2MB.
> 
> But for 64k-page arm64 kernel with CONFIG_ARM64_64K_PAGES=y and
> CONFIG_PGTABLE_LEVELS=3 , the PMD_SIZE is 512 MB, which is much larger
> than the alignment cxl_test guarantees. That results in every CXL region
> carved from that window inherits a mis-aligned start.
> 
> The DAX driver's cxl_dax_region_probe() then calls "alloc_dax_region()
> and the probe fails with -ENOMEM, with error message
> 
> """
>     cxl_dax_region dax_region1: probe with driver cxl_dax_region failed
>                                 with error -12
> """
> 
> It was hit while bringing up cxl_test on an ARM64 server with
> ARM64_64K_PAGES config.
> 
> Raise the alignment passed to "alloc"mock_res()" to the larger of
> SZ_256M and PMD_SIZE so that the mock CFMWS window is always at least as
> well-aligned as "alloc_dax_region()" require.
> 
> Signed-off-by: Richard Cheng <icheng@xxxxxxxxxx>
> Acked-by: Kai-Heng Feng <kaihengf@xxxxxxxxxx>

Reviewed-by: Dave Jiang <dave.jiang@xxxxxxxxx>

Does this need a fixes tag?

> ---
>  tools/testing/cxl/test/cxl.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/testing/cxl/test/cxl.c b/tools/testing/cxl/test/cxl.c
> index 418669927fb0..b40e4bbcc958 100644
> --- a/tools/testing/cxl/test/cxl.c
> +++ b/tools/testing/cxl/test/cxl.c
> @@ -497,7 +497,8 @@ static int populate_cedt(void)
>  		struct acpi_cedt_cfmws *window = mock_cfmws[i];
>  
>  		cfmws_elc_update(window, i);
> -		res = alloc_mock_res(window->window_size, SZ_256M);
> +		res = alloc_mock_res(window->window_size,
> +				     max_t(int, SZ_256M, PMD_SIZE));
>  		if (!res)
>  			return -ENOMEM;
>  		window->base_hpa = res->range.start;