Re: [PATCH v4] cxl/test: Enforce PMD alignment for volatile mock regions

[Richard Cheng <icheng@nvidia.com>]

On Wed, May 27, 2026 at 06:05:44PM +0800, Alison Schofield wrote:
> On Wed, May 27, 2026 at 05:03:32PM +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
> > 
> 
> checkpatch is emitting this complaint, that I believe is a false
> positive, and I'm happy to ignore versus add ugly code to appease.
> 
> WARNING: Comparisons should place the constant on the right side of the test
> #36: FILE: tools/testing/cxl/test/cxl.c:321:
> +			.window_size = SZ_256M > PMD_SIZE ? SZ_256M : PMD_SIZE,
> 
> 
> Reviewed-by: Alison Schofield <alison.schofield@intel.com>
> 
>

Hello Alison,

Thanks for your kindness,
I ran into issue when running checkpatch script, that's why I tried to edit the line in v2,
should have decleared that more clearly.

Thanks.
--Richard
 
> > Reviewed-by: Dave Jiang <dave.jiang@intel.com>
> > Acked-by: Kai-Heng Feng <kaihengf@nvidia.com>
> > Signed-off-by: Richard Cheng <icheng@nvidia.com>
> > ---
> > Changelog:
> > 
> > v3->v4:
> >     - Replace compile-time BUILD_BUG_ON() with runtime
> >       IS_ALIGNED(mock_auto_region_size, PMD_SIZE) check in
> > cxl_test_init().
> > 
> > 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 | 13 +++++++++++--
> >  1 file changed, 11 insertions(+), 2 deletions(-)
> > 
> > diff --git a/tools/testing/cxl/test/cxl.c b/tools/testing/cxl/test/cxl.c
> > index 418669927fb0..6f8fa7504cad 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,
> >  		},
> >  		.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 +1829,12 @@ static __init int cxl_test_init(void)
> >  	int rc, i;
> >  	struct range mappable;
> >  
> > +	if (!IS_ALIGNED(mock_auto_region_size, PMD_SIZE)) {
> > +		pr_err_once("mock_auto_region_size %d must be PMD-aligned\n",
> > +			    mock_auto_region_size);
> > +		return -EINVAL;
> > +	}
> > +
> >  	cxl_acpi_test();
> >  	cxl_core_test();
> >  	cxl_mem_test();
> > 
> > base-commit: 507bd4b66c85d5b65696150cc16d31ac0b2ab151
> > -- 
> > 2.43.0
> >