linux-kernel - Re: [PATCH 4/4 v5] cxl/test: Simulate an x86 Low Memory Hole for tests

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Message-ID: <aOcxZ1ju0FmB5Xi7@aschofie-mobl2.lan>
Date: Wed, 8 Oct 2025 20:52:07 -0700
From: Alison Schofield <alison.schofield@...el.com>
To: "Fabio M. De Francesco" <fabio.m.de.francesco@...ux.intel.com>
CC: <linux-cxl@...r.kernel.org>, Davidlohr Bueso <dave@...olabs.net>,
	"Jonathan Cameron" <jonathan.cameron@...wei.com>, Dave Jiang
	<dave.jiang@...el.com>, Vishal Verma <vishal.l.verma@...el.com>, Ira Weiny
	<ira.weiny@...el.com>, "Dan Williams" <dan.j.williams@...el.com>, Jonathan
 Corbet <corbet@....net>, <linux-doc@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, Gregory Price <gourry@...rry.net>, Robert
 Richter <rrichter@....com>, Cheatham Benjamin <benjamin.cheatham@....com>
Subject: Re: [PATCH 4/4 v5] cxl/test: Simulate an x86 Low Memory Hole for
 tests

On Mon, Oct 06, 2025 at 05:58:07PM +0200, Fabio M. De Francesco wrote:
> Simulate an x86 Low Memory Hole for the CXL tests by changing the first
> mock CFMWS range size to 768MB and the CXL Endpoint Decoder HPA range
> sizes to 1GB. The auto-created region of cxl-test uses mock_cfmws[0],
> therefore the LMH path in the CXL Driver will be exercised every time
> the cxl-test module is loaded.
> 
> Since mock_cfmws[0] range base address is typically different from the
> one published by the BIOS on real hardware, the driver would fail to
> create and attach CXL Regions when it's run on the mock environment
> created by cxl-tests. Furthermore, cxl-topology.sh, cxl-events.sh, and
> cxl-sanitize.sh, would also fail.
> 
> To make the above-mentioned tests succeed again, add two "mock" versions
> of platform_*() that check the HPA range start of mock_cfmws[0] instead
> of LMH_CFMWS_RANGE_START. When cxl_core calls a cxl_core exported
> function and that function is mocked by cxl_test, the call chain causes
> a circular dependency issue. Then add also two "redirect" versions of
> platform_*() to work out the circular dependency issue.

This is some amazing mockness here !!!!

Please make it easier to review and maintain by making these 2 mock
functions match their core counterparts exactly with only one exception:

s/LMH_CFMWS_RANGE_START/mock_cfmws0_range_start

Doable, right?

>  
> +static bool
> +mock_platform_cxlrd_matches_cxled(const struct cxl_root_decoder *cxlrd,
> +				  const struct cxl_endpoint_decoder *cxled)
> +{
> +	const struct range *rd_r, *ed_r;
> +	int align;
> +
> +	rd_r = &cxlrd->cxlsd.cxld.hpa_range;
> +	ed_r = &cxled->cxld.hpa_range;
> +	align = cxled->cxld.interleave_ways * SZ_256M;
> +
> +	return rd_r->start == mock_cfmws0_range_start &&
> +	       rd_r->start == ed_r->start &&
> +	       rd_r->end < (mock_cfmws0_range_start + SZ_4G) &&
> +	       rd_r->end < ed_r->end &&
> +	       IS_ALIGNED(range_len(ed_r), align);
> +}
> +
> +static bool
> +mock_platform_region_matches_cxld(const struct cxl_region_params *p,
> +				  const struct cxl_decoder *cxld)
> +{
> +	const struct range *r = &cxld->hpa_range;
> +	const struct resource *res = p->res;
> +	int align = cxld->interleave_ways * SZ_256M;
> +
> +	return res->start == mock_cfmws0_range_start &&
> +	       res->start == r->start &&
> +	       res->end < (mock_cfmws0_range_start + SZ_4G) &&
> +	       res->end < r->end &&
> +	       IS_ALIGNED(range_len(r), align);
> +}
> +
>