Re: [PATCH v3] cxl/test: Enforce PMD alignment for volatile mock regions

[Alison Schofield]

On Fri, May 22, 2026 at 01:44:57PM +0800, Richard Cheng wrote:
> cxl_test allocates synthetic CFMWS HPA windows from a gen_pool with
> SZ_256M alignment. On arm64 with CONFIG_ARM64_64K_PAGES=y and
> CONFIG_PGTABLE_LEVELS=3, PMD_SIZE is 512M, so every CXL region carved
> from a volatile window inherits a non-PMD-aligned start, and
> cxl_dax_region_probe() -> alloc_dax_region() fails:
> 
> """
>     cxl_dax_region dax_region1: probe with driver cxl_dax_region failed
>                                 with error -12
> """
> 
> Enforce that every volatile mock CFMWS is PMD-aligned in both start and
> size
> 
> Reviewed-by: Dave Jiang <dave.jiang@xxxxxxxxx>
> Acked-by: Kai-Heng Feng <kaihengf@xxxxxxxxxx>
> Signed-off-by: Richard Cheng <icheng@xxxxxxxxxx>
> ---
> Changelog:
> 
> v2->v3:
>     - Correct hunk headers
>     - Add base commit SHA
> 
> v1->v2:
>     - Reframe from "fix start alignment" to "enforce PMD invariant for
>       volatile CFMWS"
>     - Bump cfmws5.window_size to max(SZ_256M, PMD_SIZE)
>     - Gate populate_cedt() alignment on
>       ACPI_CEDT_CFMWS_RESTRICT_VOLATILE so PMEM windows stay at SZ_256M
>     - Add BUILD_BUG_ON for MOCK_AUTO_REGION_SIZE_DEFAULT v.s. PMD_SIZE
>       in cxl_test_init()
> 
> Best regards,
> Richard Cheng.
> ---
>  tools/testing/cxl/test/cxl.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/testing/cxl/test/cxl.c b/tools/testing/cxl/test/cxl.c
> index 418669927fb0..7a1105f9a0bb 100644
> --- a/tools/testing/cxl/test/cxl.c
> +++ b/tools/testing/cxl/test/cxl.c
> @@ -318,7 +318,7 @@ static struct {
>  			.restrictions = ACPI_CEDT_CFMWS_RESTRICT_HOSTONLYMEM |
>  					ACPI_CEDT_CFMWS_RESTRICT_VOLATILE,
>  			.qtg_id = FAKE_QTG_ID,
> -			.window_size = SZ_256M,
> +			.window_size = SZ_256M > PMD_SIZE ? SZ_256M : PMD_SIZE,

Why not this: max_t(resource_size_t, SZ_256M, PMD_SIZE)


>  		},
>  		.target = { 3 },
>  	},
> @@ -495,9 +495,12 @@ static int populate_cedt(void)
>  
>  	for (i = cfmws_start; i <= cfmws_end; i++) {
>  		struct acpi_cedt_cfmws *window = mock_cfmws[i];
> +		int align = SZ_256M;
>  
>  		cfmws_elc_update(window, i);
> -		res = alloc_mock_res(window->window_size, SZ_256M);
> +		if (window->restrictions & ACPI_CEDT_CFMWS_RESTRICT_VOLATILE)
> +			align = max_t(int, SZ_256M, PMD_SIZE);
> +		res = alloc_mock_res(window->window_size, align);
>  		if (!res)
>  			return -ENOMEM;
>  		window->base_hpa = res->range.start;
> @@ -1826,6 +1829,8 @@ static __init int cxl_test_init(void)
>  	int rc, i;
>  	struct range mappable;
>  
> +	BUILD_BUG_ON(!IS_ALIGNED(MOCK_AUTO_REGION_SIZE_DEFAULT, PMD_SIZE));

The rule we need to enforce is tha the actual auto region size is
PMD aligned, not the default definition. So I think this needs to
be a runtime check of IS_ALIGNED(mock_auto_region_size, PMD_SIZE).

-- Alison

> +
>  	cxl_acpi_test();
>  	cxl_core_test();
>  	cxl_mem_test();
> 
> base-commit: 6779b50faa562e6cca1aa6a4649a4d764c6c7e28
> -- 
> 2.43.0
>