linux-kernel - Re: [PATCH v4 11/14] cxl/atl: Lock decoders that need address translation

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Message-ID: <ae28560c-ed16-400b-bf3d-86e2cc8617cf@intel.com>
Date: Tue, 4 Nov 2025 10:13:34 -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 v4 11/14] cxl/atl: Lock decoders that need address
 translation

On 11/3/25 11:47 AM, Robert Richter wrote:
> There is only support to translate addresses from an endpoint to its
> CXL host bridge, but not in the opposite direction from the bridge to
> the endpoint. Thus, the endpoint address range cannot be determined
> and setup manually for a given SPA range of a region. If the endpoint
> has address translation enabled, lock it to prevent the kernel from
> reconfiguring it.
> 
> Reviewed-by: Gregory Price <gourry@...rry.net>
> Signed-off-by: Robert Richter <rrichter@....com>
> ---
>  drivers/cxl/core/atl.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/cxl/core/atl.c b/drivers/cxl/core/atl.c
> index d6aa7e6d0ac5..5c15e4d12193 100644
> --- a/drivers/cxl/core/atl.c
> +++ b/drivers/cxl/core/atl.c
> @@ -158,6 +158,16 @@ static int cxl_prm_translate_hpa_range(struct cxl_root *cxl_root, void *data)
>  		return -ENXIO;
>  	}
>  
> +	/*
> +	 * There is only support to translate from the endpoint to its
> +	 * parent port, but not in the opposite direction from the
> +	 * parent to the endpoint. Thus, the endpoint address range
> +	 * cannot be determined and setup manually. If the address range
> +	 * was translated and modified, forbid reprogramming of the
> +	 * decoders and lock them.
> +	 */
> +	cxld->flags |= CXL_DECODER_F_LOCK;

Feels like this should be something the BIOS should enforce if that is the expectation? And the kernel checks and warns if that is not the case.

> +
>  	ctx->hpa_range = hpa_range;
>  	ctx->interleave_ways = ways;
>  	ctx->interleave_granularity = gran;