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: 4423eb5ae32e ("powerpc/64/interrupt: make normal synchronous interrupts enable MSR[EE] if possible")
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220926054305.2671436-4-npiggin@gmail.com

diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c
index 0e75cb03244adefa0918b9c590e43ac8700ddf2c..f9db0a172401a5e8fd6752fb858179f0acf6a166 100644 (file)
--- a/arch/powerpc/kernel/interrupt.c
+++ b/arch/powerpc/kernel/interrupt.c
@@ -431,16 +431,6 @@ again:
 
                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 */
        }
 

diff --git a/arch/powerpc/kernel/interrupt_64.S b/arch/powerpc/kernel/interrupt_64.S
index 90dbd6a8d4dafb7ba012f58506664a155f3a4475..1dfa67e9199aafd0ec161bd19601867a1b981a4c 100644 (file)
--- a/arch/powerpc/kernel/interrupt_64.S
+++ b/arch/powerpc/kernel/interrupt_64.S
@@ -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