From 37508b63607f0b631e77f9a60516ff1c6ac2c5a7 Mon Sep 17 00:00:00 2001 Message-Id: <37508b63607f0b631e77f9a60516ff1c6ac2c5a7.1601675151.git.zanussi@kernel.org> In-Reply-To: <5b5a156f9808b1acf1205606e03da117214549ea.1601675151.git.zanussi@kernel.org> References: <5b5a156f9808b1acf1205606e03da117214549ea.1601675151.git.zanussi@kernel.org> From: Sebastian Andrzej Siewior Date: Tue, 24 Jul 2018 14:48:55 +0200 Subject: [PATCH 019/333] x86/efi: drop task_lock() from efi_switch_mm() Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.148-rt64.tar.xz 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 --- arch/x86/platform/efi/efi_64.c | 10 ++++------ 1 file changed, 4 insertions(+), 6 deletions(-) diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c index 52dd59af873e..04f05173e6ff 100644 --- a/arch/x86/platform/efi/efi_64.c +++ b/arch/x86/platform/efi/efi_64.c @@ -617,18 +617,16 @@ void __init efi_dump_pagetable(void) /* * Makes the calling thread switch to/from efi_mm context. Can be used - * for SetVirtualAddressMap() i.e. current->active_mm == init_mm as well - * as during efi runtime calls i.e current->active_mm == current_mm. - * We are not mm_dropping()/mm_grabbing() any mm, because we are not - * losing/creating any references. + * in a kernel thread and user context. Preemption needs to remain disabled + * while the EFI-mm is borrowed. mmgrab()/mmdrop() is not used because the mm + * can not change under us. + * It should be ensured that there are no concurent calls to this function. */ void efi_switch_mm(struct mm_struct *mm) { - task_lock(current); efi_scratch.prev_mm = current->active_mm; current->active_mm = mm; switch_mm(efi_scratch.prev_mm, mm, NULL); - task_unlock(current); } #ifdef CONFIG_EFI_MIXED -- 2.17.1