To workaround an errata on certain Pentium Pro CPUs, i386 disables

the local APIC in initializecpu() and re-enables it if the APIC code
decides to use the local APIC after all.  Rework this workaround
slightly so that initializecpu() won't re-disable the local APIC if
it is called after the APIC code re-enables the local APIC.

2 files changed, 26 insertions, 3 deletions

diff --git a/sys/i386/i386/initcpu.c b/sys/i386/i386/initcpu.c
index a2b9192..fa2c6e1 100644
--- a/sys/i386/i386/initcpu.c
+++ b/sys/i386/i386/initcpu.c
@@ -533,6 +533,8 @@ init_6x86MX(void)
 	intr_restore(saveintr);
 }
 
+static int ppro_apic_used = -1;
+
 static void
 init_ppro(void)
 {
@@ -541,9 +543,29 @@ init_ppro(void)
 	/*
 	 * Local APIC should be disabled if it is not going to be used.
 	 */
-	apicbase = rdmsr(MSR_APICBASE);
-	apicbase &= ~APICBASE_ENABLED;
-	wrmsr(MSR_APICBASE, apicbase);
+	if (ppro_apic_used != 1) {
+		apicbase = rdmsr(MSR_APICBASE);
+		apicbase &= ~APICBASE_ENABLED;
+		wrmsr(MSR_APICBASE, apicbase);
+		ppro_apic_used = 0;
+	}
+}
+
+/*
+ * If the local APIC is going to be used after being disabled above,
+ * re-enable it and don't disable it in the future.
+ */
+void
+ppro_reenable_apic(void)
+{
+	u_int64_t	apicbase;
+
+	if (ppro_apic_used == 0) {
+		apicbase = rdmsr(MSR_APICBASE);
+		apicbase |= APICBASE_ENABLED;
+		wrmsr(MSR_APICBASE, apicbase);
+		ppro_apic_used = 1;
+	}
 }
 
 /*
diff --git a/sys/i386/include/md_var.h b/sys/i386/include/md_var.h
index 89f8b51..8669815 100644
--- a/sys/i386/include/md_var.h
+++ b/sys/i386/include/md_var.h
@@ -109,6 +109,7 @@ int	is_physical_memory(vm_paddr_t addr);
 int	isa_nmi(int cd);
 vm_paddr_t kvtop(void *addr);
 void	panicifcpuunsupported(void);
+void	ppro_reenable_apic(void);
 void	printcpuinfo(void);
 void	setidt(int idx, alias_for_inthand_t *func, int typ, int dpl, int selec);
 int     user_dbreg_trap(void);