linux-kernel - Re: [PATCH v7 11/11] cxl/atl: Lock decoders that need address translation

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Message-ID: <9750cd82-29be-4830-8b12-9cd397dfd8a6@intel.com>
Date: Fri, 14 Nov 2025 15:05:42 -0700
From: Dave Jiang <dave.jiang@...el.com>
To: Robert Richter <rrichter@....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>,
 Jonathan Cameron <jonathan.cameron@...wei.com>,
 Davidlohr Bueso <dave@...olabs.net>
Cc: 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>, Joshua Hahn <joshua.hahnjy@...il.com>
Subject: Re: [PATCH v7 11/11] cxl/atl: Lock decoders that need address
 translation



On 11/14/25 2:39 PM, Robert Richter wrote:
> The current kernel implementation does not support endpoint setup with
> Normalized Addressing. It only translates an endpoint's DPA to the SPA
> range of the host bridge. Therefore, the endpoint address range cannot
> be determined, making a non-auto setup impossible. If a decoder
> requires address translation, reprogramming should be disabled and the
> decoder locked.
> 
> The BIOS, however, provides all the necessary address translation
> data, which the kernel can use to reconfigure endpoint decoders with
> normalized addresses. Locking the decoders in the BIOS would prevent a
> capable kernel (or other operating systems) from shutting down
> auto-generated regions and managing resources dynamically.
> 
> Reviewed-by: Gregory Price <gourry@...rry.net>
> Reviewed-by: Jonathan Cameron <jonathan.cameron@...wei.com>
> Tested-by: Gregory Price <gourry@...rry.net>
> Signed-off-by: Robert Richter <rrichter@....com>

Reviewed-by: Dave Jiang <dave.jiang@...el.com>> ---
>  drivers/cxl/core/atl.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/drivers/cxl/core/atl.c b/drivers/cxl/core/atl.c
> index 3b02999d3c59..0590890bd093 100644
> --- a/drivers/cxl/core/atl.c
> +++ b/drivers/cxl/core/atl.c
> @@ -161,6 +161,24 @@ static int cxl_prm_translate_hpa_range(struct cxl_root *cxl_root, void *data)
>  		return -ENXIO;
>  	}
>  
> +	/*
> +	 * The current kernel implementation does not support endpoint
> +	 * setup with Normalized Addressing. It only translates an
> +	 * endpoint's DPA to the SPA range of the host bridge.
> +	 * Therefore, the endpoint address range cannot be determined,
> +	 * making a non-auto setup impossible. If a decoder requires
> +	 * address translation, reprogramming should be disabled and
> +	 * the decoder locked.
> +	 *
> +	 * The BIOS, however, provides all the necessary address
> +	 * translation data, which the kernel can use to reconfigure
> +	 * endpoint decoders with normalized addresses. Locking the
> +	 * decoders in the BIOS would prevent a capable kernel (or
> +	 * other operating systems) from shutting down auto-generated
> +	 * regions and managing resources dynamically.
> +	 */
> +	cxld->flags |= CXL_DECODER_F_LOCK;
> +
>  	ctx->hpa_range = hpa_range;
>  	ctx->interleave_ways = ways;
>  	ctx->interleave_granularity = gran;