linux-kernel - Re: [PATCH 4/4 v3] cxl/test: Simulate an x86 Low Memory Hole for tests

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Message-ID: <7393617.eO5KgaWL5Y@fdefranc-mobl3>
Date: Wed, 26 Mar 2025 17:58:50 +0100
From: "Fabio M. De Francesco" <fabio.m.de.francesco@...ux.intel.com>
To: Robert Richter <rrichter@....com>
Cc: Davidlohr Bueso <dave@...olabs.net>,
 Jonathan Cameron <jonathan.cameron@...wei.com>,
 Dave Jiang <dave.jiang@...el.com>,
 Alison Schofield <alison.schofield@...el.com>,
 Vishal Verma <vishal.l.verma@...el.com>, Ira Weiny <ira.weiny@...el.com>,
 Dan Williams <dan.j.williams@...el.com>, ming.li@...omail.com,
 linux-kernel@...r.kernel.org, linux-cxl@...r.kernel.org
Subject:
 Re: [PATCH 4/4 v3] cxl/test: Simulate an x86 Low Memory Hole for tests

On Friday, March 21, 2025 11:42:09 AM Central European Standard Time Robert Richter wrote:
> On 14.03.25 12:36:33, 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.
> > 
> > Since the auto-created region of cxl-test uses mock_cfmws[0], whose 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 if
> > it was run on the mock environment created by cxl-tests.
> > 
> > Therefore, save the mock_cfmsw[0] range base_hpa and reuse it to match CXL
> > Root Decoders and Regions with Endpoint Decoders when the driver is run on
> > mock devices.
> > 
> > Since the auto-created region of cxl-test uses mock_cfmws[0], the
> > LMH path in the CXL Driver will be exercised every time the cxl-test
> > module is loaded. Executing unit test: cxl-topology.sh, confirms the
> > region created successfully with a LMH.
> > 
> > Cc: Alison Schofield <alison.schofield@...el.com>
> > Cc: Dan Williams <dan.j.williams@...el.com>
> > Cc: Ira Weiny <ira.weiny@...el.com>
> > Signed-off-by: Fabio M. De Francesco <fabio.m.de.francesco@...ux.intel.com>
> > ---
> >  drivers/cxl/core/lmh.c               | 35 ++++++++++++++++++++++++----
> >  drivers/cxl/core/lmh.h               |  2 ++
> 
> Can you take a look to move all those changes to testing/? This
> indicates the interface of your mock functions need improvement.
> 
> -Robert
> 
> >  tools/testing/cxl/cxl_core_exports.c |  2 ++
> >  tools/testing/cxl/test/cxl.c         | 10 ++++++++
> >  4 files changed, 45 insertions(+), 4 deletions(-)
> 
Your comment is not very detailed but I think you are suggesting to 
override the lmh functions in testing. If that is the case, I don't think 
that any function which is exported from and also called by cxl-core 
can be override by testing with the strong/weak mechanism. 

But I'm not an expert of linker related topics and not even sure that I 
understood what you suggested.

Would you please elaborate more?

Thanks,

Fabio

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