CVE-2026-99240: mm/damon/core: error damos_commit_quota_goal() for zero target_value

In the Linux kernel, the following vulnerability has been resolved:

mm/damon/core: error damoscommitquotagoal() for zero targetvalue

Patch series "mm/damon: move zero damos quota targetvalue handling to the core layer".

Having zero DAMOS quota target value can cause division by zero. DAMON API callers are checking the target value parameters to avoid that. It is easy to make mistakes in some of the multiple API callers. Move that to the core layer.

Patch 1 adds the corner case handling into the core layer DAMON parameters validation logic. Patches 2 and 3 remove no more needed DAMON API callers side handling of the corner case in DAMONLRUSORT and DMONSAMPLIEMTIER, respectively.

This patch (of 3):

If a DAMOS scheme has a damosquotagoal of zero targetvalue, damosquotagoal() could trigger division-by-zero error. Hence each DAMON API callers should do the zero targetvalue validation. It is easy to make mistakes. Actually such bugs in DAMONLRUSORT and DAMONSAMPLEMTIER were found and fixed [1].

It is better to handle the corner case only once in the core layer, instead of multiple places in all DAMON API callers. One straightforward option is using an alternative denominator for the corner case in the damosquotagoal(). However, the zero targetvalue is meaningless. In this case, the quota goal is always evaluated as achieved or over-achieved. The quota will only keep being reduced.

Simply avoid using zero targetvalue by adding a check in the core layer DAMOS quota goal parameters validation/commit path, damoscommitquotagoal(). Update it to return an error in the case. Also update its caller to propagate the error.