netdev - Re: [PATCH v18 09/20] cxl: Define a driver interface for HPA free space enumeration

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Message-ID: <1b18b212-d348-4a9e-aa87-0cd3db596ed8@amd.com>
Date: Mon, 22 Sep 2025 16:09:10 -0500
From: "Cheatham, Benjamin" <benjamin.cheatham@....com>
To: <alejandro.lucero-palau@....com>
CC: Jonathan Cameron <Jonathan.Cameron@...wei.com>,
	<linux-cxl@...r.kernel.org>, <netdev@...r.kernel.org>,
	<dan.j.williams@...el.com>, <edward.cree@....com>, <davem@...emloft.net>,
	<kuba@...nel.org>, <pabeni@...hat.com>, <edumazet@...gle.com>,
	<dave.jiang@...el.com>
Subject: Re: [PATCH v18 09/20] cxl: Define a driver interface for HPA free
 space enumeration

[snip]

> +
> +/**
> + * cxl_get_hpa_freespace - find a root decoder with free capacity per constraints
> + * @endpoint: the endpoint requiring the HPA
> + * @interleave_ways: number of entries in @host_bridges
> + * @flags: CXL_DECODER_F flags for selecting RAM vs PMEM, and Type2 device
> + * @max_avail_contig: output parameter of max contiguous bytes available in the
> + *		      returned decoder
> + *
> + * Returns a pointer to a struct cxl_root_decoder
> + *
> + * The return tuple of a 'struct cxl_root_decoder' and 'bytes available given
> + * in (@max_avail_contig))' is a point in time snapshot. If by the time the
> + * caller goes to use this root decoder's capacity the capacity is reduced then
s/capacity the/capacity and the

Or you could cleanup to: "If by the time the caller goes to use this root decoder
and its capacity is reduced then...".

> + * caller needs to loop and retry.
> + *
> + * The returned root decoder has an elevated reference count that needs to be
> + * put with cxl_put_root_decoder(cxlrd).
> + */
> +struct cxl_root_decoder *cxl_get_hpa_freespace(struct cxl_memdev *cxlmd,
> +					       int interleave_ways,
> +					       unsigned long flags,
> +					       resource_size_t *max_avail_contig)
> +{
> +	struct cxl_root *root __free(put_cxl_root) = NULL;
> +	struct cxl_port *endpoint = cxlmd->endpoint;
> +	struct cxlrd_max_context ctx = {
> +		.host_bridges = &endpoint->host_bridge,
> +		.flags = flags,
> +	};
> +	struct cxl_port *root_port;
> +
> +	if (!endpoint) {
> +		dev_dbg(&cxlmd->dev, "endpoint not linked to memdev\n");
> +		return ERR_PTR(-ENXIO);
> +	}

I'm 99% sure you'll crash in this case. The endpoint pointer is dereferenced when assigning to ctx above.

> +
> +	root  = find_cxl_root(endpoint);
> +	if (!root) {
> +		dev_dbg(&endpoint->dev, "endpoint can not be related to a root port\n");

s/can not/is not

> +		return ERR_PTR(-ENXIO);
> +	}
> +
> +	root_port = &root->port;
> +	scoped_guard(rwsem_read, &cxl_rwsem.region)
> +		device_for_each_child(&root_port->dev, &ctx, find_max_hpa);

Do you need the brackets for the scoped guard? I'm not sure how the macro expands when they aren't
there.