From 9b8be19d5dc9525a408942e2e8012873199e7455 Mon Sep 17 00:00:00 2001 From: Magnus Lindholm Date: Sat, 10 Oct 2026 16:24:27 +0200 Subject: [PATCH] alpha: load the MMU context when switch_mm() switches the current task ev5_switch_mm() only prepares the incoming PCB. The context is installed by PAL_swpctx, which alpha_switch_to() issues against that PCB on the way out of the scheduler. Direct callers reach switch_mm() without going through alpha_switch_to(): kthread_use_mm(), which borrows an mm for the current kernel thread, sched_force_init_mm() on the CPU-hotplug teardown path, and do_shoot_lazy_tlb(), which switches to init_mm from an IPI. None explicitly loads the context, so the task can carry on running under whatever was loaded before. For kthread_use_mm(), current->mm then names the borrowed mm even though its context has not been loaded. The other two callers change active_mm while leaving current->mm NULL. The stale page-table root need not be swapper_pg_dir; it may belong to a user process that ran on the CPU earlier, and the kthread's user accesses can then read and write that process's memory wherever the stale mappings allow. Translations taken that way can also end up tagged with the borrowed mm's ASN: ev5_switch_mm() writes that ASN into the PCB, which the next PAL_swpctx installs against the stale ptbr. An address the stale tables do not map faults instead, and since do_page_fault() resolves faults against current->mm without reloading the context, the same access can fault again on return. sched_force_init_mm() needs CONFIG_HOTPLUG_CPU and do_shoot_lazy_tlb() needs CONFIG_MMU_LAZY_TLB_SHOOTDOWN. Alpha selects neither, so only kthread_use_mm() is reachable in practice. Test the caller's identity rather than special-casing individual callers. The scheduler passes the incoming task, which is not current until alpha_switch_to() runs; all three direct callers pass current. Test for that and load the context the way activate_mm() does. All three run with interrupts disabled across the switch, so this completes before any shootdown can be taken and needs no asn_lock handshake. Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Cc: stable@vger.kernel.org Tested-by: Matt Turner Reviewed-by: Matt Turner Signed-off-by: Magnus Lindholm Link: https://lore.kernel.org/r/20261010142533.974797-2-linmag7@gmail.com Signed-off-by: Magnus Lindholm --- arch/alpha/include/asm/mmu_context.h | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) diff --git a/arch/alpha/include/asm/mmu_context.h b/arch/alpha/include/asm/mmu_context.h index eee8fe836a59..d366f89fee58 100644 --- a/arch/alpha/include/asm/mmu_context.h +++ b/arch/alpha/include/asm/mmu_context.h @@ -130,6 +130,8 @@ __get_new_mm_context(struct mm_struct *mm, long cpu) return next; } +extern void __load_new_mm_context(struct mm_struct *); + __EXTERN_INLINE void ev5_switch_mm(struct mm_struct *prev_mm, struct mm_struct *next_mm, struct task_struct *next) @@ -139,6 +141,16 @@ ev5_switch_mm(struct mm_struct *prev_mm, struct mm_struct *next_mm, unsigned long mmc; long cpu = smp_processor_id(); + /* + * kthread_use_mm(), sched_force_init_mm() and do_shoot_lazy_tlb() + * switch current's mm without alpha_switch_to(), which loads the + * context. The latter two require options Alpha does not select. + */ + if (next == current) { + __load_new_mm_context(next_mm); + return; + } + #ifdef CONFIG_SMP cpu_data[cpu].asn_lock = 1; barrier(); @@ -160,7 +172,6 @@ ev5_switch_mm(struct mm_struct *prev_mm, struct mm_struct *next_mm, task_thread_info(next)->pcb.asn = mmc & HARDWARE_ASN_MASK; } -extern void __load_new_mm_context(struct mm_struct *); asmlinkage void do_page_fault(unsigned long address, unsigned long mmcsr, long cause, struct pt_regs *regs);