[PATCH 1/1] cxl/acpi: Fix using extra xormaps for address translation

[PATCH 1/1] cxl/acpi: Fix using extra xormaps for address translation

[Li Ming]

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@zohomail.com>
---
 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

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

[Dave Jiang]

On 1/15/26 6:16 AM, 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.

Can you add what is the current impact without applying the fix pls?

DJ

> 
> Fixes: 3b2fedcd75e3 ("cxl: Restore XOR'd position bits during address translation")
> Signed-off-by: Li Ming <ming.li@zohomail.com>
> ---
>  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]);

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

[Alison Schofield]

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@zohomail.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
> 

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

[Li Ming]

在 2026/1/16 01:56, Alison Schofield 写道:
> 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@zohomail.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

Hi Alison,


Thanks for pointing it out, you are right, it is not a bug. After 
reviewing cxl_parse_cxims(), the cxmisd->xormaps stores the correct 
number of xor maps based on the interleave ways. In fact, 
nr_maps_to_apply is equal to cximsd->nr_maps in cxl_do_xormap_calc(), So 
it is not needed to change it.


Hi Alison and Dave,


Please ignore this patch, apologies for the noise.


Thanks

Ming

>
>> ---
>>   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
>>