netdev - Re: [PATCH v3 18/20] cxl: preclude device memory to be used for dax

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Message-ID: <45aeb8f4-b452-4ecf-8dcc-1b0a9f89e2ae@intel.com>
Date: Fri, 13 Sep 2024 10:26:28 -0700
From: Dave Jiang <dave.jiang@...el.com>
To: alejandro.lucero-palau@....com, linux-cxl@...r.kernel.org,
 netdev@...r.kernel.org, dan.j.williams@...el.com, martin.habets@...inx.com,
 edward.cree@....com, davem@...emloft.net, kuba@...nel.org,
 pabeni@...hat.com, edumazet@...gle.com
Cc: Alejandro Lucero <alucerop@....com>
Subject: Re: [PATCH v3 18/20] cxl: preclude device memory to be used for dax



On 9/7/24 1:18 AM, alejandro.lucero-palau@....com wrote:
> From: Alejandro Lucero <alucerop@....com>
> 
> By definition a type2 cxl device will use the host managed memory for
> specific functionality, therefore it should not be available to other
> uses.
> 
> Signed-off-by: Alejandro Lucero <alucerop@....com>
> ---
>  drivers/cxl/core/region.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> index d8c29e28e60c..45b4891035a6 100644
> --- a/drivers/cxl/core/region.c
> +++ b/drivers/cxl/core/region.c
> @@ -3699,6 +3699,9 @@ static int cxl_region_probe(struct device *dev)
>  	case CXL_DECODER_PMEM:
>  		return devm_cxl_add_pmem_region(cxlr);
>  	case CXL_DECODER_RAM:
> +		if (cxlr->type != CXL_DECODER_HOSTONLYMEM)
> +			return 0;
> +

While it's highly unlikely that someone puts pmem on a type2 device, the spec does not forbid it. Maybe it makes sense to just return 0 above this switch block entirely and skip this code block?


>  		/*
>  		 * The region can not be manged by CXL if any portion of
>  		 * it is already online as 'System RAM'