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

[Richard Cheng <icheng@nvidia.com>]

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@nvidia.com>
Acked-by: Kai-Heng Feng <kaihengf@nvidia.com>
---
 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;
-- 
2.43.0