- Add hw.clflush_disable loader tunable to avoid panic (trap 9) at

  map_invalidate_cache_range() even if CPU is not Intel.
- This tunable can be set to -1 (default), 0 and 1.  -1 is same as
  current behavior, which automatically disable CLFLUSH on Intel CPUs
  without CPUID_SS (should be occured on Xen only).  You can specify 1
  when this panic happened on non-Intel CPUs (such as AMD's).  Because
  disabling CLFLUSH may reduce performance, you can try with setting 0
  on Intel CPUs without SS to use CLFLUSH feature.

Reviewed by:	kib
Reported by:	karl, kuriyama
Related to:	kern/138863

2 files changed, 36 insertions, 2 deletions

diff --git a/sys/amd64/amd64/initcpu.c b/sys/amd64/amd64/initcpu.c
index 7aaff82..0753306 100644
--- a/sys/amd64/amd64/initcpu.c
+++ b/sys/amd64/amd64/initcpu.c
@@ -47,6 +47,13 @@ __FBSDID("$FreeBSD$");
 static int	hw_instruction_sse;
 SYSCTL_INT(_hw, OID_AUTO, instruction_sse, CTLFLAG_RD,
     &hw_instruction_sse, 0, "SIMD/MMX2 instructions available in CPU");
+/*
+ * -1: automatic (default)
+ *  0: keep enable CLFLUSH
+ *  1: force disable CLFLUSH
+ */
+static int	hw_clflush_disable = -1;
+TUNABLE_INT("hw.clflush_disable", &hw_clflush_disable);
 
 int	cpu;			/* Are we 386, 386sx, 486, etc? */
 u_int	cpu_feature;		/* Feature flags */
@@ -169,6 +176,16 @@ initializecpu(void)
 	 * XXXKIB: (temporary) hack to work around traps generated when
 	 * CLFLUSHing APIC registers window.
 	 */
-	if (cpu_vendor_id == CPU_VENDOR_INTEL && !(cpu_feature & CPUID_SS))
+	TUNABLE_INT_FETCH("hw.clflush_disable", &hw_clflush_disable);
+	if (cpu_vendor_id == CPU_VENDOR_INTEL && !(cpu_feature & CPUID_SS) &&
+	    hw_clflush_disable == -1)
+		cpu_feature &= ~CPUID_CLFSH;
+	/*
+	 * Allow to disable CLFLUSH feature manually by
+	 * hw.clflush_disable tunable.  This may help Xen guest on some AMD
+	 * CPUs.
+	 */
+	if (hw_clflush_disable == 1) {
 		cpu_feature &= ~CPUID_CLFSH;
+	}
 }
diff --git a/sys/i386/i386/initcpu.c b/sys/i386/i386/initcpu.c
index dc8da0b..bcd9922 100644
--- a/sys/i386/i386/initcpu.c
+++ b/sys/i386/i386/initcpu.c
@@ -75,6 +75,13 @@ static void	init_mendocino(void);
 static int	hw_instruction_sse;
 SYSCTL_INT(_hw, OID_AUTO, instruction_sse, CTLFLAG_RD,
     &hw_instruction_sse, 0, "SIMD/MMX2 instructions available in CPU");
+/*
+ * -1: automatic (default)
+ *  0: keep enable CLFLUSH
+ *  1: force disable CLFLUSH
+ */
+static int	hw_clflush_disable = -1;
+TUNABLE_INT("hw.clflush_disable", &hw_clflush_disable);
 
 /* Must *NOT* be BSS or locore will bzero these after setting them */
 int	cpu = 0;		/* Are we 386, 386sx, 486, etc? */
@@ -721,8 +728,18 @@ initializecpu(void)
 	 * XXXKIB: (temporary) hack to work around traps generated when
 	 * CLFLUSHing APIC registers window.
 	 */
-	if (cpu_vendor_id == CPU_VENDOR_INTEL && !(cpu_feature & CPUID_SS))
+	TUNABLE_INT_FETCH("hw.clflush_disable", &hw_clflush_disable);
+	if (cpu_vendor_id == CPU_VENDOR_INTEL && !(cpu_feature & CPUID_SS) &&
+	    hw_clflush_disable == -1)
+		cpu_feature &= ~CPUID_CLFSH;
+	/*
+	 * Allow to disable CLFLUSH feature manually by
+	 * hw.clflush_disable tunable.  This may help Xen guest on some AMD
+	 * CPUs.
+	 */
+	if (hw_clflush_disable == 1) {
 		cpu_feature &= ~CPUID_CLFSH;
+	}
 
 #if defined(PC98) && !defined(CPU_UPGRADE_HW_CACHE)
 	/*