kernel/linux.git/fs/resctrl, branch v6.18.21

x86,fs/resctrl: Fix NULL pointer dereference with events force-disabled in mbm_event mode

2025-10-20T16:06:31+00:00

The following NULL pointer dereference is encountered on mount of resctrl fs after booting a system that supports assignable counters with the "rdt=!mbmtotal,!mbmlocal" kernel parameters: BUG: kernel NULL pointer dereference, address: 0000000000000008 RIP: 0010:mbm_cntr_get Call Trace: rdtgroup_assign_cntr_event rdtgroup_assign_cntrs rdt_get_tree Specifying the kernel parameter "rdt=!mbmtotal,!mbmlocal" effectively disables the legacy X86_FEATURE_CQM_MBM_TOTAL and X86_FEATURE_CQM_MBM_LOCAL features and the MBM events they represent. This results in the per-domain MBM event related data structures to not be allocated during early initialization. resctrl fs initialization follows by implicitly enabling both MBM total and local events on a system that supports assignable counters (mbm_event mode), but this enabling occurs after the per-domain data structures have been created. After booting, resctrl fs assumes that an enabled event can access all its state. This results in NULL pointer dereference when resctrl attempts to access the un-allocated structures of an enabled event. Remove the late MBM event enabling from resctrl fs. This leaves a problem where the X86_FEATURE_CQM_MBM_TOTAL and X86_FEATURE_CQM_MBM_LOCAL features may be disabled while assignable counter (mbm_event) mode is enabled without any events to support. Switching between the "default" and "mbm_event" mode without any events is not practical. Create a dependency between the X86_FEATURE_{CQM_MBM_TOTAL,CQM_MBM_LOCAL} and X86_FEATURE_ABMC (assignable counter) hardware features. An x86 system that supports assignable counters now requires support of X86_FEATURE_CQM_MBM_TOTAL or X86_FEATURE_CQM_MBM_LOCAL. This ensures all needed MBM related data structures are created before use and that it is only possible to switch between "default" and "mbm_event" mode when the same events are available in both modes. This dependency does not exist in the hardware but this usage of these feature settings work for known systems. [ bp: Massage commit message. ] Fixes: 13390861b426e ("x86,fs/resctrl: Detect Assignable Bandwidth Monitoring feature details") Co-developed-by: Reinette Chatre Signed-off-by: Reinette Chatre Signed-off-by: Babu Moger Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Reinette Chatre Link: https://patch.msgid.link/a62e6ac063d0693475615edd213d5be5e55443e6.1760560934.git.babu.moger@amd.com

fs/resctrl: Fix counter auto-assignment on mkdir with mbm_event enabled

2025-09-17T09:31:12+00:00

rdt_resource::resctrl_mon::mbm_assign_on_mkdir determines if a counter will automatically be assigned to an RMID, MBM event pair when its associated monitor group is created via mkdir. Testing shows that counters are always automatically assigned to new monitor groups, whether mbm_assign_on_mkdir is set or not. To support automatic counter assignment the check for mbm_assign_on_mkdir should be in rdtgroup_assign_cntrs() that assigns counters during monitor group creation. Instead, the check for mbm_assign_on_mkdir is in rdtgroup_unassign_cntrs() that is called on monitor group deletion from where counters should always be unassigned, whether mbm_assign_on_mkdir is set or not. Fix automatic counter assignment by moving the mbm_assign_on_mkdir check from rdtgroup_unassign_cntrs() to rdtgroup_assign_cntrs(). [ bp: Replace commit message with Reinette's version. ] Fixes: ef712fe97ec57 ("fs/resctrl: Auto assign counters on mkdir and clean up on group removal") Signed-off-by: Babu Moger Signed-off-by: Borislav Petkov (AMD) Acked-by: Reinette Chatre

fs/resctrl: Introduce the interface to switch between monitor modes

2025-09-15T10:49:18+00:00

Resctrl subsystem can support two monitoring modes, "mbm_event" or "default". In mbm_event mode, monitoring event can only accumulate data while it is backed by a hardware counter. In "default" mode, resctrl assumes there is a hardware counter for each event within every CTRL_MON and MON group. Introduce mbm_assign_mode resctrl file to switch between mbm_event and default modes. Example: To list the MBM monitor modes supported: $ cat /sys/fs/resctrl/info/L3_MON/mbm_assign_mode [mbm_event] default To enable the "mbm_event" counter assignment mode: $ echo "mbm_event" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode To enable the "default" monitoring mode: $ echo "default" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode Reset MBM event counters automatically as part of changing the mode. Clear both architectural and non-architectural event states to prevent overflow conditions during the next event read. Clear assignable counter configuration on all the domains. Also, enable auto assignment when switching to "mbm_event" mode. Signed-off-by: Babu Moger Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Reinette Chatre Link: https://lore.kernel.org/cover.1757108044.git.babu.moger@amd.com

fs/resctrl: Disable BMEC event configuration when mbm_event mode is enabled

2025-09-15T10:48:19+00:00

The BMEC (Bandwidth Monitoring Event Configuration) feature enables per-domain event configuration. With BMEC the MBM events are configured using the mbm_total_bytes_config or mbm_local_bytes_config files in /sys/fs/resctrl/info/L3_MON/ and the per-domain event configuration affects all monitor resource groups. The mbm_event counter assignment mode enables counters to be assigned to RMID (i.e. a monitor resource group), event pairs, with potentially unique event configurations associated with every counter. There may be systems that support both BMEC and mbm_event counter assignment mode, but resctrl supporting both concurrently will present a conflicting interface to the user with both per-domain and per RMID, event configurations active at the same time. The mbm_event counter assignment provides most flexibility to user space and aligns with Arm's counter support. On systems that support both, disable BMEC event configuration when mbm_event mode is enabled by hiding the mbm_total_bytes_config or mbm_local_bytes_config files when mbm_event mode is enabled. Ensure mon_features always displays accurate information about monitor features. Suggested-by: Reinette Chatre Signed-off-by: Babu Moger Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Reinette Chatre Link: https://lore.kernel.org/cover.1757108044.git.babu.moger@amd.com

fs/resctrl: Introduce the interface to modify assignments in a group

2025-09-15T10:47:17+00:00

Enable the mbm_l3_assignments resctrl file to be used to modify counter assignments of CTRL_MON and MON groups when the "mbm_event" counter assignment mode is enabled. Process the assignment modifications in the following format: :=;= Event: A valid MBM event in the /sys/fs/resctrl/info/L3_MON/event_configs directory. Domain ID: A valid domain ID. When writing, '*' applies the changes to all domains. Assignment states: _ : Unassign a counter. e : Assign a counter exclusively. Examples: $ cd /sys/fs/resctrl $ cat /sys/fs/resctrl/mbm_L3_assignments mbm_total_bytes:0=e;1=e mbm_local_bytes:0=e;1=e To unassign the counter associated with the mbm_total_bytes event on domain 0: $ echo "mbm_total_bytes:0=_" > mbm_L3_assignments $ cat /sys/fs/resctrl/mbm_L3_assignments mbm_total_bytes:0=_;1=e mbm_local_bytes:0=e;1=e To unassign the counter associated with the mbm_total_bytes event on all the domains: $ echo "mbm_total_bytes:*=_" > mbm_L3_assignments $ cat /sys/fs/resctrl/mbm_L3_assignments mbm_total_bytes:0=_;1=_ mbm_local_bytes:0=e;1=e Signed-off-by: Babu Moger Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Reinette Chatre Link: https://lore.kernel.org/cover.1757108044.git.babu.moger@amd.com

fs/resctrl: Introduce mbm_L3_assignments to list assignments in a group

2025-09-15T10:45:34+00:00

Introduce the mbm_L3_assignments resctrl file associated with CTRL_MON and MON resource groups to display the counter assignment states of the resource group when "mbm_event" counter assignment mode is enabled. Display the list in the following format: :=;= Event: A valid MBM event listed in /sys/fs/resctrl/info/L3_MON/event_configs directory. Domain ID: A valid domain ID. The assignment state can be one of the following: _ : No counter assigned. e : Counter assigned exclusively. Example: To list the assignment states for the default group $ cd /sys/fs/resctrl $ cat /sys/fs/resctrl/mbm_L3_assignments mbm_total_bytes:0=e;1=e mbm_local_bytes:0=e;1=e Signed-off-by: Babu Moger Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Reinette Chatre Link: https://lore.kernel.org/cover.1757108044.git.babu.moger@amd.com

fs/resctrl: Auto assign counters on mkdir and clean up on group removal

2025-09-15T10:44:04+00:00

Resctrl provides a user-configurable option mbm_assign_on_mkdir that determines if a counter will automatically be assigned to an RMID, event pair when its associated monitor group is created via mkdir. Enable mbm_assign_on_mkdir by default to automatically assign counters to the two default events (MBM total and MBM local) of a new monitoring group created via mkdir. This maintains backward compatibility with original resctrl support for these two events. Unassign and free counters belonging to a monitoring group when the group is deleted. Monitor group creation does not fail if a counter cannot be assigned to one or both events. There may be limited counters and users have the flexibility to modify counter assignments at a later time. Log the error message "Failed to allocate counter for in domain " in /sys/fs/resctrl/info/last_cmd_status when a new monitoring group is created but counter assignment failed. Signed-off-by: Babu Moger Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Reinette Chatre Link: https://lore.kernel.org/cover.1757108044.git.babu.moger@amd.com

fs/resctrl: Introduce mbm_assign_on_mkdir to enable assignments on mkdir

2025-09-15T10:42:02+00:00

The "mbm_event" counter assignment mode allows users to assign a hardware counter to an RMID, event pair and monitor the bandwidth as long as it is assigned. Introduce a user-configurable option that determines if a counter will automatically be assigned to an RMID, event pair when its associated monitor group is created via mkdir. Accessible when "mbm_event" counter assignment mode is enabled. Suggested-by: Peter Newman Signed-off-by: Babu Moger Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Reinette Chatre Link: https://lore.kernel.org/cover.1757108044.git.babu.moger@amd.com

fs/resctrl: Provide interface to update the event configurations

2025-09-15T10:40:38+00:00

When "mbm_event" counter assignment mode is enabled, users can modify the event configuration by writing to the 'event_filter' resctrl file. The event configurations for mbm_event mode are located in /sys/fs/resctrl/info/L3_MON/event_configs/. Update the assignments of all CTRL_MON and MON resource groups when the event configuration is modified. Example: $ mount -t resctrl resctrl /sys/fs/resctrl $ cd /sys/fs/resctrl/ $ cat info/L3_MON/event_configs/mbm_local_bytes/event_filter local_reads,local_non_temporal_writes,local_reads_slow_memory $ echo "local_reads,local_non_temporal_writes" > info/L3_MON/event_configs/mbm_total_bytes/event_filter $ cat info/L3_MON/event_configs/mbm_total_bytes/event_filter local_reads,local_non_temporal_writes Signed-off-by: Babu Moger Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Reinette Chatre Link: https://lore.kernel.org/cover.1757108044.git.babu.moger@amd.com

fs/resctrl: Add event configuration directory under info/L3_MON/

2025-09-15T10:39:38+00:00

The "mbm_event" counter assignment mode allows the user to assign a hardware counter to an RMID, event pair and monitor the bandwidth as long as it is assigned. The user can specify the memory transaction(s) for the counter to track. When this mode is supported, the /sys/fs/resctrl/info/L3_MON/event_configs directory contains a sub-directory for each MBM event that can be assigned to a counter. The MBM event sub-directory contains a file named "event_filter" that is used to view and modify which memory transactions the MBM event is configured with. Create /sys/fs/resctrl/info/L3_MON/event_configs directory on resctrl mount and pre-populate it with directories for the two existing MBM events: mbm_total_bytes and mbm_local_bytes. Create the "event_filter" file within each MBM event directory with the needed *show() that displays the memory transactions with which the MBM event is configured. Example: $ mount -t resctrl resctrl /sys/fs/resctrl $ cd /sys/fs/resctrl/ $ cat info/L3_MON/event_configs/mbm_total_bytes/event_filter local_reads,remote_reads,local_non_temporal_writes, remote_non_temporal_writes,local_reads_slow_memory, remote_reads_slow_memory,dirty_victim_writes_all $ cat info/L3_MON/event_configs/mbm_local_bytes/event_filter local_reads,local_non_temporal_writes,local_reads_slow_memory Signed-off-by: Babu Moger Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Reinette Chatre Link: https://lore.kernel.org/cover.1757108044.git.babu.moger@amd.com