Re: tlb_gather_mmu() and semantics of "fullmm"

[David Miller <davem@davemloft.net>]

From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Date: Fri, 27 Mar 2009 16:38:07 +1100

> If you look at context_switch() in kernel/sched.c, it increments
> mm_count when using the pevious guy's mm as the "active_mm" of a kernel
> thread, not mm_user.

Yawn...

arch/sparc/include/asm/mmu_context_64.h:
static inline void switch_mm(struct mm_struct *old_mm, struct mm_struct *mm, struct task_struct *tsk)
{
...
	spin_lock_irqsave(&mm->context.lock, flags);
	ctx_valid = CTX_VALID(mm->context);
	if (!ctx_valid)
		get_new_mmu_context(mm);
 ...
	cpu = smp_processor_id();
	if (!ctx_valid || !cpu_isset(cpu, mm->cpu_vm_mask)) {
		cpu_set(cpu, mm->cpu_vm_mask);
		__flush_tlb_mm(CTX_HWBITS(mm->context),
			       SECONDARY_CONTEXT);
	}
	spin_unlock_irqrestore(&mm->context.lock, flags);
...

We unconditionally check if the CPU is set in the mask, even
when the mm isn't changing.

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