linux-kernel - Re: [PATCH] testing/cxl: Fix abused pci_bus_read_config

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Message-ID: <6716bde0a5337_3ee22944f@dwillia2-xfh.jf.intel.com.notmuch>
Date: Mon, 21 Oct 2024 13:47:28 -0700
From: Dan Williams <dan.j.williams@...el.com>
To: Ira Weiny <ira.weiny@...el.com>, "Zhijian Li (Fujitsu)"
	<lizhijian@...itsu.com>, Dan Williams <dan.j.williams@...el.com>, "Alison
 Schofield" <alison.schofield@...el.com>
CC: "linux-cxl@...r.kernel.org" <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>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "Huang, Ying" <ying.huang@...el.com>
Subject: Re: [PATCH] testing/cxl: Fix abused pci_bus_read_config_word() on
 platform device

Ira Weiny wrote:
[..]
> > --- a/drivers/cxl/core/cdat.c
> > +++ b/drivers/cxl/core/cdat.c
> > @@ -5,6 +5,7 @@
> >    #include <linux/fw_table.h>
> >    #include <linux/node.h>
> >    #include <linux/overflow.h>
> > +#include <linux/platform_device.h>
> >    #include "cxlpci.h"
> >    #include "cxlmem.h"
> >    #include "core.h"
> > @@ -641,9 +642,13 @@ static int cxl_endpoint_gather_bandwidth(struct cxl_region *cxlr,
> >           void *ptr;
> >           int rc;
> > 
> > +       if (dev_is_pci(cxlds->dev))
> 
> Did you mean...
> 
> 	if (!dev_is_pci(cxlds->dev))
> ???

Yes, skip non-PCI.

[..]
> Couldn't this be done on the endpoint call?  (Making it non-static?)
> 
> int __wrap_cxl_endpoint_gather_bandwidth(...
>                                          struct cxl_endpoint_decoder *cxled,
> 					...)
> {
>         struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
>         struct cxl_dev_state *cxlds = cxlmd->cxlds;
> 
> 	if (!dev_is_pci(cxlds->dev))
> 		return -ENODEV;
> 
> 	return cxl_endpoint_gather_bandwidth(...);
> }

No, cxl_endpoint_gather_bandwidth() is called internal to cxl_core,
there is no opportunity to optionally wrap it, only replace it.

In order for this path to be mocked the cxl_region driver would need to
be moved to a module and then
cxl_region_shared_upstream_bandwidth_update() could be unit tested.