x86/hpet: warn about and clear reserved set config register bits

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/hpet.c
+++ b/xen/arch/x86/hpet.c
@@ -755,6 +755,13 @@ void hpet_resume(u32 *boot_cfg)
     if ( boot_cfg )
         *boot_cfg = cfg;
     cfg &= ~(HPET_CFG_ENABLE | HPET_CFG_LEGACY);
+    if ( cfg )
+    {
+        printk(XENLOG_WARNING
+               "HPET: reserved bits %#x set in global config register\n",
+               cfg);
+        cfg = 0;
+    }
     hpet_write32(cfg, HPET_CFG);
 
     hpet_id = hpet_read32(HPET_ID);
@@ -765,6 +772,13 @@ void hpet_resume(u32 *boot_cfg)
         if ( boot_cfg )
             boot_cfg[i + 1] = cfg;
         cfg &= ~HPET_TN_ENABLE;
+        if ( cfg & HPET_TN_RESERVED )
+        {
+            printk(XENLOG_WARNING
+                   "HPET: reserved bits %#x set in channel %u config register\n",
+                   cfg & HPET_TN_RESERVED, i);
+            cfg &= ~HPET_TN_RESERVED;
+        }
         hpet_write32(cfg, HPET_Tn_CFG(i));
     }
 
--- a/xen/arch/x86/hvm/hpet.c
+++ b/xen/arch/x86/hvm/hpet.c
@@ -42,7 +42,8 @@
     (hvm_get_guest_time(vhpet_vcpu(hpet)) / STIME_PER_HPET_TICK)
 
 #define HPET_TN_INT_ROUTE_CAP_SHIFT 32
-#define HPET_TN_CFG_BITS_READONLY_OR_RESERVED 0xffff80b1U
+#define HPET_TN_CFG_BITS_READONLY_OR_RESERVED (HPET_TN_RESERVED | \
+    HPET_TN_PERIODIC_CAP | HPET_TN_64BIT_CAP | HPET_TN_FSB_CAP)
 
 /* can be routed to IOAPIC.redirect_table[23..20] */
 #define HPET_TN_INT_ROUTE_CAP      (0x00f00000ULL \
--- a/xen/include/asm-x86/hpet.h
+++ b/xen/include/asm-x86/hpet.h
@@ -43,6 +43,7 @@
 #define HPET_TN_ROUTE		0x3e00
 #define HPET_TN_FSB		0x4000
 #define HPET_TN_FSB_CAP		0x8000
+#define HPET_TN_RESERVED	0xffff0081
 #define HPET_TN_ROUTE_SHIFT	9