linux-kernel - Re: [PATCH v4 03/14] cxl/pci: Add comments to cxl_hdm_decode

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <20250314113337.000054b6@huawei.com>
Date: Fri, 14 Mar 2025 11:33:37 +0000
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Robert Richter <rrichter@....com>
CC: 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>, Dave Jiang <dave.jiang@...el.com>, "Davidlohr
 Bueso" <dave@...olabs.net>, <linux-cxl@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, Gregory Price <gourry@...rry.net>, "Fabio M.
 De Francesco" <fabio.m.de.francesco@...ux.intel.com>, Terry Bowman
	<terry.bowman@....com>
Subject: Re: [PATCH v4 03/14] cxl/pci: Add comments to cxl_hdm_decode_init()

On Thu, 6 Mar 2025 17:44:37 +0100
Robert Richter <rrichter@....com> wrote:

> There are various configuration cases of HDM decoder registers causing
> different code paths. Add comments to cxl_hdm_decode_init() to better
> explain them.
> 
> Signed-off-by: Robert Richter <rrichter@....com>
> Tested-by: Gregory Price <gourry@...rry.net>
Trivial comment inline.
Otherwise I think this is fine.
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>

> ---
>  drivers/cxl/core/pci.c | 33 ++++++++++++++++++++++++---------
>  1 file changed, 24 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/cxl/core/pci.c b/drivers/cxl/core/pci.c
> index 6386e84e51a4..ef4b08abe424 100644
> --- a/drivers/cxl/core/pci.c
> +++ b/drivers/cxl/core/pci.c
> @@ -416,9 +416,21 @@ int cxl_hdm_decode_init(struct cxl_dev_state *cxlds, struct cxl_hdm *cxlhdm,
>  	if (global_ctrl & CXL_HDM_DECODER_ENABLE || (!hdm && info->mem_enabled))
>  		return devm_cxl_enable_mem(&port->dev, cxlds);
>  
> +	/*
> +	 * If the HDM Decoder Capability does not exist and DVSEC was
> +	 * not setup, the DVSEC based emulation cannot be used.
> +	 */
>  	if (!hdm)
>  		return -ENODEV;
>  
> +	/*
> +	 * The HDM Decoder Capability exists but is globally disabled.

Single line comment syntax appropriate here.

> +	 */
> +
> +	/*
> +	 * If the DVSEC CXL Range registers are not enabled, just
> +	 * enable and use the HDM Decoder Capability registers.
> +	 */
>  	if (!info->mem_enabled) {
>  		rc = devm_cxl_enable_hdm(&port->dev, cxlhdm);
>  		if (rc)
> @@ -427,6 +439,18 @@ int cxl_hdm_decode_init(struct cxl_dev_state *cxlds, struct cxl_hdm *cxlhdm,
>  		return devm_cxl_enable_mem(&port->dev, cxlds);
>  	}
>  
> +	/*
> +	 * Per CXL 2.0 Section 8.1.3.8.3 and 8.1.3.8.4 DVSEC CXL Range 1 Base
> +	 * [High,Low] when HDM operation is enabled the range register values
> +	 * are ignored by the device, but the spec also recommends matching the
> +	 * DVSEC Range 1,2 to HDM Decoder Range 0,1. So, non-zero info->ranges
> +	 * are expected even though Linux does not require or maintain that
> +	 * match. Check if at least one DVSEC range is enabled and allowed by
> +	 * the platform. That is, the DVSEC range must be covered by a locked
> +	 * platform window (CFMWS). Fail otherwise as the endpoint's decoders
> +	 * cannot be used.
> +	 */
> +
>  	root = to_cxl_port(port->dev.parent);
>  	while (!is_cxl_root(root) && is_cxl_port(root->dev.parent))
>  		root = to_cxl_port(root->dev.parent);
> @@ -454,15 +478,6 @@ int cxl_hdm_decode_init(struct cxl_dev_state *cxlds, struct cxl_hdm *cxlhdm,
>  		return -ENXIO;
>  	}
>  
> -	/*
> -	 * Per CXL 2.0 Section 8.1.3.8.3 and 8.1.3.8.4 DVSEC CXL Range 1 Base
> -	 * [High,Low] when HDM operation is enabled the range register values
> -	 * are ignored by the device, but the spec also recommends matching the
> -	 * DVSEC Range 1,2 to HDM Decoder Range 0,1. So, non-zero info->ranges
> -	 * are expected even though Linux does not require or maintain that
> -	 * match. If at least one DVSEC range is enabled and allowed, skip HDM
> -	 * Decoder Capability Enable.
> -	 */
>  	return 0;
>  }
>  EXPORT_SYMBOL_NS_GPL(cxl_hdm_decode_init, "CXL");