Commit dc398a08 authored by Nicholas Piggin's avatar Nicholas Piggin Committed by Michael Ellerman
Browse files

powerpc/64s/interrupt: Perf NMI should not take normal exit path 



NMI interrupts should exit with EXCEPTION_RESTORE_REGS not with
interrupt_return_srr, which is what the perf NMI handler currently does.
This breaks if a PMI hits after interrupt_exit_user_prepare_main() has
switched the context tracking to user mode, then the CT_WARN_ON() in
interrupt_exit_kernel_prepare() fires because it returns to kernel with
context set to user.

This could possibly be solved by soft-disabling PMIs in the exit path,
but that reduces our ability to profile that code. The warning could be
removed, but it's potentially useful.

All other NMIs and soft-NMIs return using EXCEPTION_RESTORE_REGS, so
this makes perf interrupts consistent with that and seems like the best
fix.

Signed-off-by: default avatarNicholas Piggin <npiggin@gmail.com>
[mpe: Squash in fixups from Nick]
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20221006140413.126443-3-npiggin@gmail.com
parent a073672e

arch/powerpc/kernel/exceptions-64s.S

+13 −1
Original line number Diff line number Diff line
@@ -2357,9 +2357,21 @@ EXC_VIRT_END(performance_monitor, 0x4f00, 0x20) 
EXC_COMMON_BEGIN(performance_monitor_common)

	GEN_COMMON performance_monitor

	addi	r3,r1,STACK_FRAME_OVERHEAD

	bl	performance_monitor_exception

	lbz	r4,PACAIRQSOFTMASK(r13)

	cmpdi	r4,IRQS_ENABLED

	bne	1f

	bl	performance_monitor_exception_async

	b	interrupt_return_srr

1:

	bl	performance_monitor_exception_nmi

	/* Clear MSR_RI before setting SRR0 and SRR1. */

	li	r9,0

	mtmsrd	r9,1



	kuap_kernel_restore r9, r10



	EXCEPTION_RESTORE_REGS hsrr=0

	RFI_TO_KERNEL



/**

 * Interrupt 0xf20 - Vector Unavailable Interrupt.

arch/powerpc/kernel/interrupt.c

+8 −6
Original line number Diff line number Diff line
@@ -377,13 +377,15 @@ notrace unsigned long interrupt_exit_kernel_prepare(struct pt_regs *regs) 
	 * CT_WARN_ON comes here via program_check_exception, so avoid

	 * recursion.

	 *

	 * Skip the assertion on PMIs to work around a problem caused by NMI

	 * PMIs incorrectly taking this interrupt return path, it's possible

	 * for this to hit after interrupt exit to user switches context to

	 * user. See also the comment in the performance monitor handler in

	 * exceptions-64e/s.S

	 * Skip the assertion on PMIs on 64e to work around a problem caused

	 * by NMI PMIs incorrectly taking this interrupt return path, it's

	 * possible for this to hit after interrupt exit to user switches

	 * context to user. See also the comment in the performance monitor

	 * handler in exceptions-64e.S

	 */

	if (TRAP(regs) != INTERRUPT_PROGRAM && TRAP(regs) != INTERRUPT_PERFMON)

	if (!IS_ENABLED(CONFIG_PPC_BOOK3E_64) &&

	    TRAP(regs) != INTERRUPT_PROGRAM &&

	    TRAP(regs) != INTERRUPT_PERFMON)

		CT_WARN_ON(ct_state() == CONTEXT_USER);



	kuap = kuap_get_and_assert_locked();