Re: [PATCH v2 1/2] cxl/hdm: Allow zero sized HDM decoders

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Skipping devm_cxl_dpa_reserve() for zero-size decoders leaves port->hdm_end un-incremented, causing the out-of-order DPA allocation check to fail unconditionally for subsequent decoders.
--

commit 413b72f0366d77ee154e5fec85ab5deab385b5af
Author: Richard Cheng <icheng@nvidia.com>

cxl/hdm: Allow zero sized HDM decoders
    
This commit allows committing an HDM decoder with a size of 0 to support BIOS
configurations that burn slots for Trusted Computing Base devices. It sets
port->commit_end before checking for a zero size and skips
devm_cxl_dpa_reserve() for these decoders since they have no DPA range to
reserve.

> diff --git a/drivers/cxl/core/hdm.c b/drivers/cxl/core/hdm.c
> index 0c80b76a5f9b4..467ac45bee553 100644
> --- a/drivers/cxl/core/hdm.c
> +++ b/drivers/cxl/core/hdm.c

[ ... ]

> @@ -1096,6 +1095,10 @@ static int init_hdm_decoder(struct cxl_port *port, struct cxl_decoder *cxld,
>  	if (!committed)
>  		return 0;
>  
> +	/* Committed zero-size decoder has nothing to reserve in DPA. */
> +	if (size == 0)
> +		return 0;
> +

[Severity: High]
Does skipping devm_cxl_dpa_reserve() here prevent port->hdm_end from being
incremented for the zero-size decoder?

If port->hdm_end is not updated, won't subsequent decoders fail the DPA
reservation path?

drivers/cxl/core/hdm.c:__cxl_dpa_reserve() {
    ...
	if (port->hdm_end + 1 != cxled->cxld.id) {
		/*
		 * Assumes alloc and commit order is always in hardware instance
		 * order...
		 */
		dev_dbg(dev, "decoder%d.%d: expected decoder%d.%d\n", port->id,
			cxled->cxld.id, port->id, port->hdm_end + 1);
		return -EBUSY;
	}
    ...
}

If a zero-size decoder (e.g. ID N) skips the reserve step, port->hdm_end stays
at N-1. When decoder N+1 tries to reserve DPA, port->hdm_end + 1 is N, which
does not match N+1, causing an unconditional -EBUSY.

>  	dpa_size = div_u64_rem(size, cxld->interleave_ways, &remainder);
>  	if (remainder) {
>  		dev_err(&port->dev,

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/cover.1779957270.git.icheng@nvidia.com?part=1