From 60c53f565454a6afd8f0b80d36d791d50653751d Mon Sep 17 00:00:00 2001
From: Damien Zammit <damien@zamaudio.com>
Date: Mon, 2 Oct 2023 03:39:13 +0000
Subject: Fix interrupt handling

Logic for interrupts:

- interrupt.S raises spl (thus IF cleared)
- interrupt.S EOI
- interrupt.S calls the handler
   - for pure in-kernel handlers, they do whatever they want with IF
     cleared.
   - when a userland handler is registers, queue_intr masks the irq.
- interrupt.S lowers spl with splx_cli, thus IF still cleared
- iret, that sets IF

- later on, userland acks the IRQ, that unmasks the irq

The key to this change is that all interrupts, including IPIs, are
treated the same way. Eg. the spl level is now raised before an IPI and
restored after. Also, EOI is not needed inside irq_acknowledge.

With this change and the experimental change not to dispatch threads
direct to idle processors in the scheduler, I no longer observe kernel
faults, but an occasional hang does occur.

Message-Id: <20231002033906.124427-1-damien@zamaudio.com>
---
 i386/i386at/interrupt.S | 28 +++++++++++++---------------
 1 file changed, 13 insertions(+), 15 deletions(-)

(limited to 'i386')

diff --git a/i386/i386at/interrupt.S b/i386/i386at/interrupt.S
index 8ae6b97c..77424b43 100644
--- a/i386/i386at/interrupt.S
+++ b/i386/i386at/interrupt.S
@@ -45,14 +45,6 @@ ENTRY(interrupt)
 	ret				/* if so, just return */
 1:
 #endif
-#if NCPUS > 1
-	cmpl	$CALL_PMAP_UPDATE,%eax	/* was this a SMP pmap_update request? */
-	je	_call_single
-
-	cmpl	$CALL_AST_CHECK,%eax	/* was this a SMP remote -> local ast request? */
-	je	_call_local_ast
-#endif
-
 	subl	$24,%esp		/* Two local variables + 4 parameters */
 	movl	%eax,S_IRQ		/* save irq number */
 
@@ -61,6 +53,14 @@ ENTRY(interrupt)
 
 	movl	S_IRQ,%ecx		/* restore irq number */
 
+#if NCPUS > 1
+	cmpl	$CALL_PMAP_UPDATE,%ecx	/* was this a SMP pmap_update request? */
+	je	_call_single
+
+	cmpl	$CALL_AST_CHECK,%ecx	/* was this a SMP remote -> local ast request? */
+	je	_call_local_ast
+#endif
+
 #ifndef APIC
 	movl	$1,%eax
 	shll	%cl,%eax		/* get corresponding IRQ mask */
@@ -98,11 +98,8 @@ ENTRY(interrupt)
 	outb	%al,$(PIC_MASTER_OCW)	/* unmask master */
 2:
 #else
-	cmpl    $16,%ecx		/* was this a low ISA intr? */
-	jge     _no_eoi			/* no, must be PCI (let irq_ack handle EOI) */
 	movl	%ecx,(%esp)		/* load irq number as 1st arg */
 	call	EXT(ioapic_irq_eoi)	/* ioapic irq specific EOI */
-_no_eoi:
 #endif
 
 	movl	S_IPL,%eax
@@ -122,6 +119,7 @@ _no_eoi:
 
 	call	*EXT(ivect)(%eax)	/* call interrupt handler */
 
+_completed:
 	movl	S_IPL,%eax		/* restore previous ipl */
 	movl	%eax,(%esp)
 	call	splx_cli		/* restore previous ipl */
@@ -131,14 +129,14 @@ _no_eoi:
 
 #if NCPUS > 1
 _call_single:
-	cli				/* no nested interrupts */
 	call	EXT(lapic_eoi)		/* lapic EOI before the handler to allow extra update */
 	call	EXT(pmap_update_interrupt)
-	ret
+	jmp	_completed
 
 _call_local_ast:
-	call	EXT(ast_check)		/* AST check on this cpu */
 	call	EXT(lapic_eoi)		/* lapic EOI */
-	ret
+	call	EXT(ast_check)		/* AST check on this cpu */
+	jmp	_completed
+
 #endif
 END(interrupt)
-- 
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