[PATCH 1 of 6] APIC: record local APIC state on boot

[Andrew Cooper <andrew.cooper3@citrix.com>]

Xen does not store the boot local APIC state which leads to problems
when shutting down for a kexec jump.  This patch records the boot
state so we can return to the boot state when kexec'ing.

Section 3.8 of the MultiProcessor spec states that when the bios hands
over to the operating system, all AP locals APICs should be disabled, and
the BSP local APIC is up to the bios with regards to compatability.
Therefore, we only need to record the BSP mode.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>

diff -r 37c77bacb52a -r 8d30fccc0771 xen/arch/x86/apic.c
--- a/xen/arch/x86/apic.c	Mon May 23 17:38:28 2011 +0100
+++ b/xen/arch/x86/apic.c	Wed May 25 15:10:24 2011 +0100
@@ -74,6 +74,8 @@ u8 __read_mostly apic_verbosity;
 static bool_t __initdata opt_x2apic = 1;
 boolean_param("x2apic", opt_x2apic);
 
+enum apic_mode __read_mostly apic_boot_mode = APIC_MODE_INVALID;
+
 bool_t __read_mostly x2apic_enabled = 0;
 bool_t __read_mostly directed_eoi_enabled = 0;
 
@@ -1437,8 +1439,64 @@ int __init APIC_init_uniprocessor (void)
     return 0;
 }
 
+/* Needs to be called once per CPU during startup.  It records the state the BIOS
+ * leaves the local APIC so we can tare back down upon shutdown/crash
+ */
+void __init record_boot_APIC_mode(void)
+{
+
+    /* Sanity check - we should only ever run once, but could possibly be called
+     * several times */
+    if( APIC_MODE_INVALID != apic_boot_mode )
+        return;
+
+    apic_boot_mode = current_local_apic_mode();
+
+    apic_printk(APIC_DEBUG, "APIC boot state is '%s' on core #%d\n",
+                apic_mode_to_str(apic_boot_mode), smp_processor_id());
+}
+
+/* Look at the bits in MSR_IA32_APICBASE and work out which APIC mode we are in */
+const enum apic_mode current_local_apic_mode(void)
+{
+    u64 msr_contents;
+
+    rdmsrl(MSR_IA32_APICBASE, msr_contents);
+
+    /* Reading EXTD bit from the MSR is only valid if CPUID says so, else reserved */
+    if ( cpu_has(&current_cpu_data, X86_FEATURE_X2APIC)
+         && (msr_contents & MSR_IA32_APICBASE_EXTD) )
+        return APIC_MODE_X2APIC;
+    else
+        {
+            /* EN bit should always be valid as long as we can read the MSR
+             */
+            if ( msr_contents & MSR_IA32_APICBASE_ENABLE )
+                return APIC_MODE_XAPIC;
+            else
+                return APIC_MODE_DISABLED;
+        }
+}
+
 void check_for_unexpected_msi(unsigned int vector)
 {
     unsigned long v = apic_read(APIC_ISR + ((vector & ~0x1f) >> 1));
     BUG_ON(v & (1 << (vector & 0x1f)));
 }
+
+const char * apic_mode_to_str(const enum apic_mode mode)
+{
+    switch(mode)
+        {
+        case APIC_MODE_INVALID:
+            return "invalid";
+        case APIC_MODE_DISABLED:
+            return "disabled";
+        case APIC_MODE_XAPIC:
+            return "xapic";
+        case APIC_MODE_X2APIC:
+            return "x2apic";
+        default:
+            return "unrecognised";
+        }
+}
diff -r 37c77bacb52a -r 8d30fccc0771 xen/arch/x86/genapic/probe.c
--- a/xen/arch/x86/genapic/probe.c	Mon May 23 17:38:28 2011 +0100
+++ b/xen/arch/x86/genapic/probe.c	Wed May 25 15:10:24 2011 +0100
@@ -60,6 +60,8 @@ void __init generic_apic_probe(void)
 { 
 	int i, changed;
 
+    record_boot_APIC_mode();
+
 	check_x2apic_preenabled();
 	cmdline_apic = changed = (genapic != NULL);
 
diff -r 37c77bacb52a -r 8d30fccc0771 xen/include/asm-x86/apic.h
--- a/xen/include/asm-x86/apic.h	Mon May 23 17:38:28 2011 +0100
+++ b/xen/include/asm-x86/apic.h	Wed May 25 15:10:24 2011 +0100
@@ -21,6 +21,19 @@
 #define IO_APIC_REDIR_DEST_LOGICAL	0x00800
 #define IO_APIC_REDIR_DEST_PHYSICAL	0x00000
 
+/* Possible APIC states */
+enum apic_mode { APIC_MODE_INVALID,  /* Not set yet */
+                 APIC_MODE_DISABLED, /* Some bioses disable by default for compatability */
+                 APIC_MODE_XAPIC,    /* xAPIC mode - default upon chipset reset */
+                 APIC_MODE_X2APIC    /* x2APIC mode - common for large smp machines */
+};
+
+/* Bootstrap processor local APIC boot mode - so we can taredown to bios state */
+extern enum apic_mode apic_boot_mode;
+
+/* enum apic_mode -> str function for logging/debug */
+const char * apic_mode_to_str(const enum apic_mode);
+
 extern u8 apic_verbosity;
 extern bool_t x2apic_enabled;
 extern bool_t directed_eoi_enabled;
@@ -203,6 +216,8 @@ extern void disable_APIC_timer(void);
 extern void enable_APIC_timer(void);
 extern int lapic_suspend(void);
 extern int lapic_resume(void);
+extern void record_boot_APIC_mode(void);
+extern const enum apic_mode current_local_apic_mode(void);
 
 extern int check_nmi_watchdog (void);