linux-kernel - Re: [PATCH 1/1] cxl/acpi: Fix using extra xormaps for address translation

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Message-ID: <aWkqVFud7UA5CRie@aschofie-mobl2.lan>
Date: Thu, 15 Jan 2026 09:56:36 -0800
From: Alison Schofield <alison.schofield@...el.com>
To: Li Ming <ming.li@...omail.com>
CC: <dave@...olabs.net>, <jonathan.cameron@...wei.com>,
	<dave.jiang@...el.com>, <vishal.l.verma@...el.com>, <ira.weiny@...el.com>,
	<dan.j.williams@...el.com>, <linux-cxl@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] cxl/acpi: Fix using extra xormaps for address
 translation

On Thu, Jan 15, 2026 at 09:16:48PM +0800, Li Ming wrote:
> CXL r3.1 Table 9-22 defines a fixed number of XOR maps for interleave
> arithmetic based on the number of interleave ways, as reflected by
> hbiw_to_nr_maps[].
> 
> The current implementation applies all XOR maps during address
> translation, but it should use the spec-defined number of XOR maps
> derived from the number of interleave ways.
> 
> Fixes: 3b2fedcd75e3 ("cxl: Restore XOR'd position bits during address translation")
> Signed-off-by: Li Ming <ming.li@...omail.com>

Ming,

I previously sent similar patch and then recalled it for the reason
described in this thread.
https://lore.kernel.org/linux-cxl/26c7ca6f-eb5f-4f20-8dba-e62e43e3e1b5@intel.com

The above was all before
	"4fe516d2ad1a6 cxl/acpi: Make the XOR calculations available for testing"
where I added input param checking and introduced nr_maps_to_apply.

I don't think it is necessary to use nr_maps_to_apply in the
for loop once the params have been validated. So maybe this patch
is a cleanup on commit 4fe516d2ad1a6 rather than a fix.

Please take a look again and let me know if I'm wrong again ;)

--Alison

> ---
>  drivers/cxl/acpi.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/cxl/acpi.c b/drivers/cxl/acpi.c
> index 77ac940e3013..5f84d01e7d39 100644
> --- a/drivers/cxl/acpi.c
> +++ b/drivers/cxl/acpi.c
> @@ -61,7 +61,7 @@ u64 cxl_do_xormap_calc(struct cxl_cxims_data *cximsd, u64 addr, int hbiw)
>  	 * bits results in val==0, if odd the XOR result is val==1.
>  	 */
>  
> -	for (int i = 0; i < cximsd->nr_maps; i++) {
> +	for (int i = 0; i < nr_maps_to_apply; i++) {
>  		if (!cximsd->xormaps[i])
>  			continue;
>  		pos = __ffs(cximsd->xormaps[i]);
> -- 
> 2.34.1
>