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efi/x86: drop task_lock() from efi_switch_mm()
efi_switch_mm() is a wrapper around switch_mm() which saves current's ->active_mm, sets the requests mm as ->active_mm and invokes switch_mm(). I don't think that task_lock() is required during that procedure. It protects ->mm which isn't changed here. It needs to be mentioned that during the whole procedure (switch to EFI's mm and back) the preemption needs to be disabled. A context switch at this point would reset the cr3 value based on current->mm. Also, this function may not be invoked at the same time on a different CPU because it would overwrite the efi_scratch.prev_mm information. Remove task_lock() and also update the comment to reflect it. Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
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@ -619,18 +619,16 @@ void __init efi_dump_pagetable(void)
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/*
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* Makes the calling thread switch to/from efi_mm context. Can be used
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* for SetVirtualAddressMap() i.e. current->active_mm == init_mm as well
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* as during efi runtime calls i.e current->active_mm == current_mm.
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* We are not mm_dropping()/mm_grabbing() any mm, because we are not
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* losing/creating any references.
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* in a kernel thread and user context. Preemption needs to remain disabled
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* while the EFI-mm is borrowed. mmgrab()/mmdrop() is not used because the mm
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* can not change under us.
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* It should be ensured that there are no concurent calls to this function.
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*/
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void efi_switch_mm(struct mm_struct *mm)
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{
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task_lock(current);
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efi_scratch.prev_mm = current->active_mm;
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current->active_mm = mm;
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switch_mm(efi_scratch.prev_mm, mm, NULL);
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task_unlock(current);
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}
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#ifdef CONFIG_EFI_MIXED
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