From: Ben Horgan Date: Fri, 13 Mar 2026 14:45:58 +0000 (+0000) Subject: arm_mpam: resctrl: Hide CDP emulation behind CONFIG_EXPERT X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=01a0021f6c39557037bfc41ede7230a0696677ff;p=thirdparty%2Fkernel%2Flinux.git arm_mpam: resctrl: Hide CDP emulation behind CONFIG_EXPERT When CDP is not enabled, the 'rmid_entry's in the limbo list, rmid_busy_llc, map directly to a (PARTID,PMG) pair and when CDP is enabled the mapping is to two different pairs. As the limbo list is reused between mounts and CDP disabled on unmount this can lead to stale mapping and the limbo handler will then make monitor reads with potentially out of range PARTID. This may then cause an MPAM error interrupt and the driver will disable MPAM. No problems are expected if you just mount the resctrl file system once with CDP enabled and never unmount it. Hide CDP emulation behind CONFIG_EXPERT to protect the unwary. Signed-off-by: Ben Horgan Reviewed-by: Gavin Shan Reviewed-by: Zeng Heng Reviewed-by: James Morse Tested-by: Gavin Shan Tested-by: Shaopeng Tan Tested-by: Jesse Chick Signed-off-by: James Morse --- diff --git a/drivers/resctrl/mpam_resctrl.c b/drivers/resctrl/mpam_resctrl.c index 2111542f485e1..2331e6ddb814b 100644 --- a/drivers/resctrl/mpam_resctrl.c +++ b/drivers/resctrl/mpam_resctrl.c @@ -82,6 +82,18 @@ int resctrl_arch_set_cdp_enabled(enum resctrl_res_level rid, bool enable) u32 partid_i = RESCTRL_RESERVED_CLOSID, partid_d = RESCTRL_RESERVED_CLOSID; int cpu; + if (!IS_ENABLED(CONFIG_EXPERT) && enable) { + /* + * If the resctrl fs is mounted more than once, sequentially, + * then CDP can lead to the use of out of range PARTIDs. + */ + pr_warn("CDP not supported\n"); + return -EOPNOTSUPP; + } + + if (enable) + pr_warn("CDP is an expert feature and may cause MPAM to malfunction.\n"); + /* * resctrl_arch_set_cdp_enabled() is only called with enable set to * false on error and unmount.