6.9-stable review patch. If anyone has any objections, please let me know.
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From: Dave Martin Dave.Martin@arm.com
[ Upstream commit 739c9765793e5794578a64aab293c58607f1826a ]
Commit
6791e0ea3071 ("x86/resctrl: Access per-rmid structures by index")
adds logic to map individual monitoring groups into a global index space used for tracking allocated RMIDs.
Attempts to free the default RMID are ignored in free_rmid(), and this works fine on x86.
With arm64 MPAM, there is a latent bug here however: on platforms with no monitors exposed through resctrl, each control group still gets a different monitoring group ID as seen by the hardware, since the CLOSID always forms part of the monitoring group ID.
This means that when removing a control group, the code may try to free this group's default monitoring group RMID for real. If there are no monitors however, the RMID tracking table rmid_ptrs[] would be a waste of memory and is never allocated, leading to a splat when free_rmid() tries to dereference the table.
One option would be to treat RMID 0 as special for every CLOSID, but this would be ugly since bookkeeping still needs to be done for these monitoring group IDs when there are monitors present in the hardware.
Instead, add a gating check of resctrl_arch_mon_capable() in free_rmid(), and just do nothing if the hardware doesn't have monitors.
This fix mirrors the gating checks already present in mkdir_rdt_prepare_rmid_alloc() and elsewhere.
No functional change on x86.
[ bp: Massage commit message. ]
Fixes: 6791e0ea3071 ("x86/resctrl: Access per-rmid structures by index") Signed-off-by: Dave Martin Dave.Martin@arm.com Signed-off-by: Borislav Petkov (AMD) bp@alien8.de Reviewed-by: Reinette Chatre reinette.chatre@intel.com Tested-by: Reinette Chatre reinette.chatre@intel.com Link: https://lore.kernel.org/r/20240618140152.83154-1-Dave.Martin@arm.com Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/kernel/cpu/resctrl/monitor.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c index c34a35ec0f031..2ce5f4913c820 100644 --- a/arch/x86/kernel/cpu/resctrl/monitor.c +++ b/arch/x86/kernel/cpu/resctrl/monitor.c @@ -508,7 +508,8 @@ void free_rmid(u32 closid, u32 rmid) * allows architectures that ignore the closid parameter to avoid an * unnecessary check. */ - if (idx == resctrl_arch_rmid_idx_encode(RESCTRL_RESERVED_CLOSID, + if (!resctrl_arch_mon_capable() || + idx == resctrl_arch_rmid_idx_encode(RESCTRL_RESERVED_CLOSID, RESCTRL_RESERVED_RMID)) return;