Commit 2a9b3e6a authored by Mark Rutland's avatar Mark Rutland Committed by Will Deacon
Browse files

arm64: entry: fix EL1 debug transitions 



In debug_exception_enter() and debug_exception_exit() we trace hardirqs
on/off while RCU isn't guaranteed to be watching, and we don't save and
restore the hardirq state, and so may return with this having changed.

Handle this appropriately with new entry/exit helpers which do the bare
minimum to ensure this is appropriately maintained, without marking
debug exceptions as NMIs. These are placed in entry-common.c with the
other entry/exit helpers.

In future we'll want to reconsider whether some debug exceptions should
be NMIs, but this will require a significant refactoring, and for now
this should prevent issues with lockdep and RCU.

Signed-off-by: default avatarMark Rutland <mark.rutland@arm.com>
Cc: Catalin Marins <catalin.marinas@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20201130115950.22492-12-mark.rutland@arm.com


Signed-off-by: default avatarWill Deacon <will@kernel.org>
parent f0cd5ac1

arch/arm64/kernel/entry-common.c

+26 −0
Original line number Diff line number Diff line
@@ -150,6 +150,30 @@ static void noinstr el1_inv(struct pt_regs *regs, unsigned long esr) 
	exit_to_kernel_mode(regs);

}



static void noinstr arm64_enter_el1_dbg(struct pt_regs *regs)

{

	regs->lockdep_hardirqs = lockdep_hardirqs_enabled();



	lockdep_hardirqs_off(CALLER_ADDR0);

	rcu_nmi_enter();



	trace_hardirqs_off_finish();

}



static void noinstr arm64_exit_el1_dbg(struct pt_regs *regs)

{

	bool restore = regs->lockdep_hardirqs;



	if (restore) {

		trace_hardirqs_on_prepare();

		lockdep_hardirqs_on_prepare(CALLER_ADDR0);

	}



	rcu_nmi_exit();

	if (restore)

		lockdep_hardirqs_on(CALLER_ADDR0);

}



static void noinstr el1_dbg(struct pt_regs *regs, unsigned long esr)

{

	unsigned long far = read_sysreg(far_el1);
@@ -162,7 +186,9 @@ static void noinstr el1_dbg(struct pt_regs *regs, unsigned long esr) 
	if (system_uses_irq_prio_masking())

		gic_write_pmr(GIC_PRIO_IRQON | GIC_PRIO_PSR_I_SET);



	arm64_enter_el1_dbg(regs);

	do_debug_exception(far, esr, regs);

	arm64_exit_el1_dbg(regs);

}



static void noinstr el1_fpac(struct pt_regs *regs, unsigned long esr)

arch/arm64/mm/fault.c

+0 −25
Original line number Diff line number Diff line
@@ -789,23 +789,6 @@ void __init hook_debug_fault_code(int nr, 
 */

static void debug_exception_enter(struct pt_regs *regs)

{

	if (!user_mode(regs)) {

		/*

		 * Tell lockdep we disabled irqs in entry.S. Do nothing if they were

		 * already disabled to preserve the last enabled/disabled addresses.

		 */

		if (interrupts_enabled(regs))

			trace_hardirqs_off();



		/*

		 * We might have interrupted pretty much anything.  In

		 * fact, if we're a debug exception, we can even interrupt

		 * NMI processing. We don't want this code makes in_nmi()

		 * to return true, but we need to notify RCU.

		 */

		rcu_nmi_enter();

	}



	preempt_disable();



	/* This code is a bit fragile.  Test it. */
@@ -816,14 +799,6 @@ NOKPROBE_SYMBOL(debug_exception_enter); 
static void debug_exception_exit(struct pt_regs *regs)

{

	preempt_enable_no_resched();



	if (user_mode(regs))

		return;



	rcu_nmi_exit();



	if (interrupts_enabled(regs))

		trace_hardirqs_on();

}

NOKPROBE_SYMBOL(debug_exception_exit);

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