59 lines
2.5 KiB
Diff
59 lines
2.5 KiB
Diff
From 37508b63607f0b631e77f9a60516ff1c6ac2c5a7 Mon Sep 17 00:00:00 2001
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Message-Id: <37508b63607f0b631e77f9a60516ff1c6ac2c5a7.1601675151.git.zanussi@kernel.org>
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In-Reply-To: <5b5a156f9808b1acf1205606e03da117214549ea.1601675151.git.zanussi@kernel.org>
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References: <5b5a156f9808b1acf1205606e03da117214549ea.1601675151.git.zanussi@kernel.org>
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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Date: Tue, 24 Jul 2018 14:48:55 +0200
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Subject: [PATCH 019/333] x86/efi: drop task_lock() from efi_switch_mm()
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Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.148-rt64.tar.xz
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efi_switch_mm() is a wrapper around switch_mm() which saves current's
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->active_mm, sets the requests mm as ->active_mm and invokes
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switch_mm().
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I don't think that task_lock() is required during that procedure. It
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protects ->mm which isn't changed here.
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It needs to be mentioned that during the whole procedure (switch to
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EFI's mm and back) the preemption needs to be disabled. A context switch
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at this point would reset the cr3 value based on current->mm. Also, this
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function may not be invoked at the same time on a different CPU because
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it would overwrite the efi_scratch.prev_mm information.
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Remove task_lock() and also update the comment to reflect it.
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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---
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arch/x86/platform/efi/efi_64.c | 10 ++++------
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1 file changed, 4 insertions(+), 6 deletions(-)
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diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
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index 52dd59af873e..04f05173e6ff 100644
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--- a/arch/x86/platform/efi/efi_64.c
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+++ b/arch/x86/platform/efi/efi_64.c
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@@ -617,18 +617,16 @@ 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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--
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2.17.1
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