Patch "arm64: entry: fix context tracking for el0_sp_pc" has been added to the 4.1-stable tree
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This is a note to let you know that I've just added the patch titled
arm64: entry: fix context tracking for el0_sp_pc
to the 4.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
arm64-entry-fix-context-tracking-for-el0_sp_pc.patch
and it can be found in the queue-4.1 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.
Quoted 1 line
From
46b0567c851cf85d6ba6f23eef385ec9111d09bcMon Sep 17 00:00:00 2001
From: Mark Rutland <[email protected]>
Date: Mon, 15 Jun 2015 16:40:27 +0100
Subject: arm64: entry: fix context tracking for el0_sp_pc
From: Mark Rutland <[email protected]>
commit 46b0567c851cf85d6ba6f23eef385ec9111d09bc upstream.
Commit 6c81fe7925cc4c42 ("arm64: enable context tracking") did not update el0_sp_pc to use ct_user_exit, but this appears to have been unintentional. In commit 6ab6463aeb5fbc75 ("arm64: adjust el0_sync so that a function can be called") we made x0 available, and in the return to userspace we call ct_user_enter in the kernel_exit macro.
Due to this, we currently don't correctly inform RCU of the user->kernel transition, and may erroneously account for time spent in the kernel as if we were in an extended quiescent state when CONFIG_CONTEXT_TRACKING is enabled.
As we do record the kernel->user transition, a userspace application making accesses from an unaligned stack pointer can demonstrate the imbalance, provoking the following warning:
------------[ cut here ]------------ WARNING: CPU: 2 PID: 3660 at kernel/context_tracking.c:75 context_tracking_enter+0xd8/0xe4() Modules linked in: CPU: 2 PID: 3660 Comm: a.out Not tainted 4.1.0-rc7+ #8 Hardware name: ARM Juno development board (r0) (DT) Call trace: [<ffffffc000089914>] dump_backtrace+0x0/0x124 [<ffffffc000089a48>] show_stack+0x10/0x1c [<ffffffc0005b3cbc>] dump_stack+0x84/0xc8 [<ffffffc0000b3214>] warn_slowpath_common+0x98/0xd0 [<ffffffc0000b330c>] warn_slowpath_null+0x14/0x20 [<ffffffc00013ada4>] context_tracking_enter+0xd4/0xe4 [<ffffffc0005b534c>] preempt_schedule_irq+0xd4/0x114 [<ffffffc00008561c>] el1_preempt+0x4/0x28 [<ffffffc0001b8040>] exit_files+0x38/0x4c [<ffffffc0000b5b94>] do_exit+0x430/0x978 [<ffffffc0000b614c>] do_group_exit+0x40/0xd4 [<ffffffc0000c0208>] get_signal+0x23c/0x4f4 [<ffffffc0000890b4>] do_signal+0x1ac/0x518 [<ffffffc000089650>] do_notify_resume+0x5c/0x68 ---[ end trace 963c192600337066 ]---
This patch adds the missing ct_user_exit to the el0_sp_pc entry path, correcting the context tracking for this case.
--- arch/arm64/kernel/entry.S | 1 + 1 file changed, 1 insertion(+)
arch/arm64/kernel/entry.S +1 -0
@@ -517,6 +517,7 @@ el0_sp_pc: mrs x26, far_el1 // enable interrupts before calling the main handler enable_dbg_and_irq + ct_user_exit mov x0, x26 mov x1, x25 mov x2, sp
Patches currently in stable-queue which might be from [email protected] are
queue-4.1/arm64-entry-fix-context-tracking-for-el0_sp_pc.patch