powerpc/64s: Implement interrupt exit logic in C

Implement the bulk of interrupt return logic in C. The asm return code
must handle a few cases: restoring full GPRs, and emulating stack
store.

The stack store emulation is significantly simplfied, rather than
creating a new return frame and switching to that before performing
the store, it uses the PACA to keep a scratch register around to
perform the store.

The asm return code is moved into 64e for now. The new logic has made
allowance for 64e, but I don't have a full environment that works well
to test it, and even booting in emulated qemu is not great for stress
testing. 64e shouldn't be too far off working with this, given a bit
more testing and auditing of the logic.

This is slightly faster on a POWER9 (page fault speed increases about
1.1%), probably due to reduced mtmsrd.

mpe: Includes fixes from Nick for _TIF_EMULATE_STACK_STORE
handling (including the fast_interrupt_return path), to remove
trace_hardirqs_on(), and fixes the interrupt-return part of the
MSR_VSX restore bug caught by tm-unavailable selftest.

mpe: Incorporate fix from Nick:

The return-to-kernel path has to replay any soft-pending interrupts if
it is returning to a context that had interrupts soft-enabled. It has
to do this carefully and avoid plain enabling interrupts if this is an
irq context, which can cause multiple nesting of interrupts on the
stack, and other unexpected issues.

The code which avoided this case got the soft-mask state wrong, and
marked interrupts as enabled before going around again to retry. This
seems to be mostly harmless except when PREEMPT=y, this calls
preempt_schedule_irq with irqs apparently enabled and runs into a BUG
in kernel/sched/core.c

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michal Suchanek <msuchanek@suse.de>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200225173541.1549955-29-npiggin@gmail.com

1 files changed, 4 insertions, 32 deletions

diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c
index 2e5dca87b936..a25ed47087ee 100644
--- a/arch/powerpc/kernel/irq.c
+++ b/arch/powerpc/kernel/irq.c
@@ -110,6 +110,8 @@ static inline notrace int decrementer_check_overflow(void)
 	return now >= *next_tb;
 }
 
+#ifdef CONFIG_PPC_BOOK3E
+
 /* This is called whenever we are re-enabling interrupts
  * and returns either 0 (nothing to do) or 500/900/280/a00/e80 if
  * there's an EE, DEC or DBELL to generate.
@@ -169,41 +171,16 @@ notrace unsigned int __check_irq_replay(void)
 		}
 	}
 
-	/*
-	 * Force the delivery of pending soft-disabled interrupts on PS3.
-	 * Any HV call will have this side effect.
-	 */
-	if (firmware_has_feature(FW_FEATURE_PS3_LV1)) {
-		u64 tmp, tmp2;
-		lv1_get_version_info(&tmp, &tmp2);
-	}
-
-	/*
-	 * Check if an hypervisor Maintenance interrupt happened.
-	 * This is a higher priority interrupt than the others, so
-	 * replay it first.
-	 */
-	if (happened & PACA_IRQ_HMI) {
-		local_paca->irq_happened &= ~PACA_IRQ_HMI;
-		return 0xe60;
-	}
-
 	if (happened & PACA_IRQ_DEC) {
 		local_paca->irq_happened &= ~PACA_IRQ_DEC;
 		return 0x900;
 	}
 
-	if (happened & PACA_IRQ_PMI) {
-		local_paca->irq_happened &= ~PACA_IRQ_PMI;
-		return 0xf00;
-	}
-
 	if (happened & PACA_IRQ_EE) {
 		local_paca->irq_happened &= ~PACA_IRQ_EE;
 		return 0x500;
 	}
 
-#ifdef CONFIG_PPC_BOOK3E
 	/*
 	 * Check if an EPR external interrupt happened this bit is typically
 	 * set if we need to handle another "edge" interrupt from within the
@@ -218,20 +195,15 @@ notrace unsigned int __check_irq_replay(void)
 		local_paca->irq_happened &= ~PACA_IRQ_DBELL;
 		return 0x280;
 	}
-#else
-	if (happened & PACA_IRQ_DBELL) {
-		local_paca->irq_happened &= ~PACA_IRQ_DBELL;
-		return 0xa00;
-	}
-#endif /* CONFIG_PPC_BOOK3E */
 
 	/* There should be nothing left ! */
 	BUG_ON(local_paca->irq_happened != 0);
 
 	return 0;
 }
+#endif /* CONFIG_PPC_BOOK3E */
 
-static void replay_soft_interrupts(void)
+void replay_soft_interrupts(void)
 {
 	/*
 	 * We use local_paca rather than get_paca() to avoid all