From 362c84a08a1b8f1eb7f9c1c37c6ed7cece348ee4 Mon Sep 17 00:00:00 2001
From: Samuel Thibault <samuel.thibault@ens-lyon.org>
Date: Thu, 10 Aug 2023 19:18:43 +0200
Subject: Acknowledge IRQ *before* calling the handler

5da1aea7ab3c ("Acknoledge interrupt after handler call") moved the IRQ ack
to after calling the handler because of overflows. But that was because the
interrupts were getting enabled at some point. Now that all spl levels
above 0 just disable interrupts, once we have called spl7 we are safe
until splx_cli is called (and even that doesn't release interrupts, only
the eventual iret will).

And if the handler triggers another IRQ, it will be lost, so we do want
to ack the IRQ before handling it.
---
 x86_64/interrupt.S | 47 ++++++++++++++++++++++++-----------------------
 1 file changed, 24 insertions(+), 23 deletions(-)

(limited to 'x86_64')

diff --git a/x86_64/interrupt.S b/x86_64/interrupt.S
index 845e0d1a..c73b31e8 100644
--- a/x86_64/interrupt.S
+++ b/x86_64/interrupt.S
@@ -41,7 +41,9 @@
 ENTRY(interrupt)
 #ifdef APIC
 	cmpl	$255,%eax		/* was this a spurious intr? */
-	je	_no_eoi			/* if so, just return */
+	jne	1f
+	ret				/* if so, just return */
+1:
 #endif
 	cmpl	$CALL_SINGLE_FUNCTION_BASE,%eax	/* was this a SMP call single function request? */
 	je	_call_single
@@ -52,26 +54,6 @@ ENTRY(interrupt)
 	call	spl7			/* set ipl */
 	movl	%eax,S_IPL		/* save previous ipl */
 
-	;
-	movq	S_IPL,S_ARG1		/* previous ipl as 2nd arg */
-
-	;
-	movq	S_RET,S_ARG2		/* return address as 3th arg */
-
-	;
-	movq	S_REGS,S_ARG3		/* address of interrupted registers as 4th arg */
-
-	movl	S_IRQ,%eax		/* copy irq number */
-	shll	$2,%eax			/* irq * 4 */
-	movl	EXT(iunit)(%rax),%edi	/* get device unit number as 1st arg */
-
-	shll	$1,%eax			/* irq * 8 */
-	call	*EXT(ivect)(%rax)	/* call interrupt handler */
-
-	movl	S_IPL,%edi		/* restore previous ipl */
-	call	splx_cli		/* restore previous ipl */
-	cli				/* XXX no more nested interrupts */
-
 	movl	S_IRQ,%ecx		/* restore irq number */
 
 #ifndef APIC
@@ -113,12 +95,31 @@ ENTRY(interrupt)
 #else
 	cmpl    $16,%ecx		/* was this a low ISA intr? */
 	jge      _no_eoi		/* no, must be PCI (let irq_ack handle EOI) */
-_isa_eoi:
 	movl	%ecx,%edi		/* load irq number as 1st arg */
 	call	EXT(ioapic_irq_eoi)	/* ioapic irq specific EOI */
+_no_eoi:
 #endif
+
+	;
+	movq	S_IPL,S_ARG1		/* previous ipl as 2nd arg */
+
+	;
+	movq	S_RET,S_ARG2		/* return address as 3th arg */
+
+	;
+	movq	S_REGS,S_ARG3		/* address of interrupted registers as 4th arg */
+
+	movl	S_IRQ,%eax		/* copy irq number */
+	shll	$2,%eax			/* irq * 4 */
+	movl	EXT(iunit)(%rax),%edi	/* get device unit number as 1st arg */
+
+	shll	$1,%eax			/* irq * 8 */
+	call	*EXT(ivect)(%rax)	/* call interrupt handler */
+
+	movl	S_IPL,%edi		/* restore previous ipl */
+	call	splx_cli		/* restore previous ipl */
+
 	addq	$16,%rsp		/* pop local variables */
-_no_eoi:
 	ret
 
 _call_single:
-- 
cgit v1.2.3