[v4,2/4] x86/APIC: make connections between seemingly arbitrary numbers

Commit Message

Jan Beulich March 31, 2022, 9:30 a.m. UTC

Making adjustments to arbitrarily chosen values shouldn't require
auditing the code for possible derived numbers - such a change should
be doable in a single place, having an effect on all code depending on
that choice.

For one make the TDCR write actually use APIC_DIVISOR. With the
necessary mask constant introduced, also use that in vLAPIC code. While
introducing the constant, drop APIC_TDR_DIV_TMBASE: The bit has been
undefined in halfway recent SDM and PM versions.

And then introduce a constant tying together the scale used when
converting nanoseconds to bus clocks.

No functional change intended.

Signed-off-by: Jan Beulich <[e-mail]>
Reviewed-by: Roger Pau Monné <[e-mail]>
---
v3: Introduce and use PASTE() instead of (ab)using _AC().
v2: New.

Patch

--- a/xen/arch/x86/apic.c
+++ b/xen/arch/x86/apic.c
@@ -1078,8 +1078,8 @@  static void __setup_APIC_LVTT(unsigned i
     lvtt_value = APIC_TIMER_MODE_ONESHOT | LOCAL_TIMER_VECTOR;
     apic_write(APIC_LVTT, lvtt_value);
 
-    tmp_value = apic_read(APIC_TDCR);
-    apic_write(APIC_TDCR, tmp_value | APIC_TDR_DIV_1);
+    tmp_value = apic_read(APIC_TDCR) & ~APIC_TDR_DIV_MASK;
+    apic_write(APIC_TDCR, tmp_value | PASTE(APIC_TDR_DIV_, APIC_DIVISOR));
 
     apic_write(APIC_TMICT, clocks / APIC_DIVISOR);
 }
@@ -1212,6 +1212,8 @@  uint32_t __init apic_tmcct_read(void)
  * APIC irq that way.
  */
 
+#define BUS_SCALE_SHIFT 18
+
 static void __init calibrate_APIC_clock(void)
 {
     unsigned long bus_freq; /* KAF: pointer-size avoids compile warns. */
@@ -1265,8 +1267,8 @@  static void __init calibrate_APIC_clock(
     /* set up multipliers for accurate timer code */
     bus_cycle  = 1000000000000UL / bus_freq; /* in pico seconds */
     bus_cycle += (1000000000000UL % bus_freq) * 2 > bus_freq;
-    bus_scale  = (1000*262144)/bus_cycle;
-    bus_scale += ((1000 * 262144) % bus_cycle) * 2 > bus_cycle;
+    bus_scale  = (1000 << BUS_SCALE_SHIFT) / bus_cycle;
+    bus_scale += ((1000 << BUS_SCALE_SHIFT) % bus_cycle) * 2 > bus_cycle;
 
     apic_printk(APIC_VERBOSE, "..... bus_scale = %#x\n", bus_scale);
     /* reset APIC to zero timeout value */
@@ -1353,7 +1355,8 @@  int reprogram_timer(s_time_t timeout)
     }
 
     if ( timeout && ((expire = timeout - NOW()) > 0) )
-        apic_tmict = min_t(u64, (bus_scale * expire) >> 18, UINT_MAX);
+        apic_tmict = min_t(uint64_t, (bus_scale * expire) >> BUS_SCALE_SHIFT,
+                           UINT32_MAX);
 
     apic_write(APIC_TMICT, (unsigned long)apic_tmict);
 
--- a/xen/arch/x86/hvm/vlapic.c
+++ b/xen/arch/x86/hvm/vlapic.c
@@ -580,7 +580,7 @@  static uint32_t vlapic_get_tmcct(const s
 static void vlapic_set_tdcr(struct vlapic *vlapic, unsigned int val)
 {
     /* Only bits 0, 1 and 3 are settable; others are MBZ. */
-    val &= 0xb;
+    val &= APIC_TDR_DIV_MASK;
     vlapic_set_reg(vlapic, APIC_TDCR, val);
 
     /* Update the demangled hw.timer_divisor. */
@@ -888,7 +888,7 @@  void vlapic_reg_write(struct vcpu *v, un
     {
         uint32_t current_divisor = vlapic->hw.timer_divisor;
 
-        vlapic_set_tdcr(vlapic, val & 0xb);
+        vlapic_set_tdcr(vlapic, val);
 
         vlapic_update_timer(vlapic, vlapic_get_reg(vlapic, APIC_LVTT), false,
                             current_divisor);
@@ -1020,7 +1020,7 @@  int guest_wrmsr_x2apic(struct vcpu *v, u
         break;
 
     case APIC_TDCR:
-        if ( msr_content & ~APIC_TDR_DIV_1 )
+        if ( msr_content & ~APIC_TDR_DIV_MASK )
             return X86EMUL_EXCEPTION;
         break;
 
--- a/xen/arch/x86/include/asm/apicdef.h
+++ b/xen/arch/x86/include/asm/apicdef.h
@@ -106,7 +106,7 @@ 
 #define		APIC_TMICT	0x380
 #define		APIC_TMCCT	0x390
 #define		APIC_TDCR	0x3E0
-#define			APIC_TDR_DIV_TMBASE	(1<<2)
+#define			APIC_TDR_DIV_MASK	0xB
 #define			APIC_TDR_DIV_1		0xB
 #define			APIC_TDR_DIV_2		0x0
 #define			APIC_TDR_DIV_4		0x1
--- a/xen/include/xen/lib.h
+++ b/xen/include/xen/lib.h
@@ -13,6 +13,10 @@ 
 #define count_args(args...) \
     count_args_(., ## args, 8, 7, 6, 5, 4, 3, 2, 1, 0)
 
+/* Indirect macros required for expanded argument pasting. */
+#define PASTE_(a, b) a ## b
+#define PASTE(a, b) PASTE_(a, b)
+
 #ifndef __ASSEMBLY__
 
 #include <xen/inttypes.h>