Commit e485f6c7 authored by Nicholas Piggin's avatar Nicholas Piggin Committed by Michael Ellerman
Browse files

powerpc/64/interrupt: Fix return to masked context after hard-mask irq becomes pending 



If a synchronous interrupt (e.g., hash fault) is taken inside an
irqs-disabled region which has MSR[EE]=1, then an asynchronous interrupt
that is PACA_IRQ_MUST_HARD_MASK (e.g., PMI) is taken inside the
synchronous interrupt handler, then the synchronous interrupt will
return with MSR[EE]=1 and the asynchronous interrupt fires again.

If the asynchronous interrupt is a PMI and the original context does not
have PMIs disabled (only Linux IRQs), the asynchronous interrupt will
fire despite having the PMI marked soft pending. This can confuse the
perf code and cause warnings.

This patch changes the interrupt return so that irqs-disabled MSR[EE]=1
contexts will be returned to with MSR[EE]=0 if a PACA_IRQ_MUST_HARD_MASK
interrupt has become pending in the meantime.

The longer explanation for what happens:
1. local_irq_disable()
2. Hash fault interrupt fires, do_hash_fault handler runs
3. interrupt_enter_prepare() sets IRQS_ALL_DISABLED
4. interrupt_enter_prepare() sets MSR[EE]=1
5. PMU interrupt fires, masked handler runs
6. Masked handler marks PMI pending
7. Masked handler returns with PACA_IRQ_HARD_DIS set, MSR[EE]=0
8. do_hash_fault interrupt return handler runs
9. interrupt_exit_kernel_prepare() clears PACA_IRQ_HARD_DIS
10. interrupt returns with MSR[EE]=1
11. PMU interrupt fires, perf handler runs

Fixes: 4423eb5a ("powerpc/64/interrupt: make normal synchronous interrupts enable MSR[EE] if possible")
Signed-off-by: default avatarNicholas Piggin <npiggin@gmail.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220926054305.2671436-4-npiggin@gmail.com
parent 799f7063

arch/powerpc/kernel/interrupt.c

+0 −10
Original line number Diff line number Diff line
@@ -431,16 +431,6 @@ notrace unsigned long interrupt_exit_kernel_prepare(struct pt_regs *regs) 


		if (unlikely(stack_store))

			__hard_EE_RI_disable();

		/*

		 * Returning to a kernel context with local irqs disabled.

		 * Here, if EE was enabled in the interrupted context, enable

		 * it on return as well. A problem exists here where a soft

		 * masked interrupt may have cleared MSR[EE] and set HARD_DIS

		 * here, and it will still exist on return to the caller. This

		 * will be resolved by the masked interrupt firing again.

		 */

		if (regs->msr & MSR_EE)

			local_paca->irq_happened &= ~PACA_IRQ_HARD_DIS;

#endif /* CONFIG_PPC64 */

	}

arch/powerpc/kernel/interrupt_64.S

+31 −3
Original line number Diff line number Diff line
@@ -526,15 +526,43 @@ _ASM_NOKPROBE_SYMBOL(interrupt_return_\srr\()_kernel) 
	ld	r11,SOFTE(r1)

	cmpwi	r11,IRQS_ENABLED

	stb	r11,PACAIRQSOFTMASK(r13)

	bne	1f

	beq	.Linterrupt_return_\srr\()_soft_enabled



	/*

	 * Returning to soft-disabled context.

	 * Check if a MUST_HARD_MASK interrupt has become pending, in which

	 * case we need to disable MSR[EE] in the return context.

	 */

	ld	r12,_MSR(r1)

	andi.	r10,r12,MSR_EE

	beq	.Lfast_kernel_interrupt_return_\srr\() // EE already disabled

	lbz	r11,PACAIRQHAPPENED(r13)

	andi.	r10,r11,PACA_IRQ_MUST_HARD_MASK

	beq	1f // No HARD_MASK pending



	/* Must clear MSR_EE from _MSR */

#ifdef CONFIG_PPC_BOOK3S

	li	r10,0

	/* Clear valid before changing _MSR */

	.ifc \srr,srr

	stb	r10,PACASRR_VALID(r13)

	.else

	stb	r10,PACAHSRR_VALID(r13)

	.endif

#endif

	xori	r12,r12,MSR_EE

	std	r12,_MSR(r1)

	b	.Lfast_kernel_interrupt_return_\srr\()



.Linterrupt_return_\srr\()_soft_enabled:

#ifdef CONFIG_PPC_BOOK3S

	lbz	r11,PACAIRQHAPPENED(r13)

	andi.	r11,r11,(~PACA_IRQ_HARD_DIS)@l

	bne-	interrupt_return_\srr\()_kernel_restart

#endif

	li	r11,0

	stb	r11,PACAIRQHAPPENED(r13) # clear out possible HARD_DIS

1:

	li	r11,0

	stb	r11,PACAIRQHAPPENED(r13) // clear the possible HARD_DIS



.Lfast_kernel_interrupt_return_\srr\():

	cmpdi	cr1,r3,0