From e105fa42d5ddb6ff7bfbbb964c4b93415b22b05a Mon Sep 17 00:00:00 2001
From: Ian Moffett <ian@osmora.org>
Date: Fri, 21 Nov 2025 14:20:15 -0500
Subject: kern: Improve IRQ mask modification on spinlocks

Signed-off-by: Ian Moffett <ian@osmora.org>
---
 sys/arch/amd64/cpu/cpu.c      | 10 ++++++++++
 sys/arch/amd64/cpu/spinlock.c | 16 ++++++++++------
 2 files changed, 20 insertions(+), 6 deletions(-)

(limited to 'sys/arch/amd64')

diff --git a/sys/arch/amd64/cpu/cpu.c b/sys/arch/amd64/cpu/cpu.c
index 4edc850..d9093fd 100644
--- a/sys/arch/amd64/cpu/cpu.c
+++ b/sys/arch/amd64/cpu/cpu.c
@@ -29,11 +29,21 @@
 
 #include <sys/types.h>
 #include <sys/cdefs.h>
+#include <sys/param.h>
 #include <os/trace.h>
 #include <mu/cpu.h>
 #include <md/msr.h>
 #include <md/lapic.h>
 
+bool
+mu_irq_state(void)
+{
+    uint64_t rflags;
+
+    __asmv("pushfq; pop %0" : "=r" (rflags) :: "memory");
+    return ISSET(rflags, BIT(9)) != 0;
+}
+
 struct cpu_info *
 cpu_self(void)
 {
diff --git a/sys/arch/amd64/cpu/spinlock.c b/sys/arch/amd64/cpu/spinlock.c
index 1cfa088..6857aa6 100644
--- a/sys/arch/amd64/cpu/spinlock.c
+++ b/sys/arch/amd64/cpu/spinlock.c
@@ -29,12 +29,15 @@
 
 #include <sys/cdefs.h>
 #include <mu/spinlock.h>
+#include <mu/irq.h>
 
 void
 mu_spinlock_acq(volatile size_t *lock, int flags)
 {
-    if (ISSET(flags, SPINLOCK_INTTOG)) {
-        asm volatile("cli");
+    bool irq_en = mu_irq_state();
+
+    if (ISSET(flags, SPINLOCK_INTTOG) && irq_en) {
+        __asmv("cli");
     }
 
     __asmv(
@@ -48,6 +51,11 @@ mu_spinlock_acq(volatile size_t *lock, int flags)
         : "r" (lock)
         : "memory", "rax"
     );
+
+    if (ISSET(flags, SPINLOCK_INTTOG)) {
+        if (irq_en && !mu_irq_state())
+            __asmv("sti");
+    }
 }
 
 void
@@ -60,8 +68,4 @@ mu_spinlock_rel(volatile size_t *lock, int flags)
         :
         : "memory", "rax"
     );
-
-    if (ISSET(flags, SPINLOCK_INTTOG)) {
-        asm volatile("sti");
-    }
 }
-- 
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