From: Rik van Riel <riel@redhat.com>
Date: Mon, 13 Apr 2009 12:10:35 -0400
Subject: [xen] x86: fix overflow in the hpet code
Message-id: 20090413121035.5cb84515@bree.surriel.com
O-Subject: [RHEL 5.4 PATCH 5/5] fix overflow in the hpet code (bz 449346)
Bugzilla: 449346
RH-Acked-by: Justin M. Forbes <jforbes@redhat.com>
RH-Acked-by: Chris Lalancette <clalance@redhat.com>
RH-Acked-by: Don Dutile <ddutile@redhat.com>

hvm: hpet: Fix overflow when converting to nanoseconds.

May not be strictly necessary, but all testing has been done with this
patch and it is a trivial overflow fix.

Fixes bug 449346

# HG changeset patch
# User Keir Fraser <keir.fraser@citrix.com>
# Date 1199809204 0
# Node ID 9ff64d045e61e7db6844b3db473e660e8c7e0551
# Parent  9865d5e82802fda2ac842c0c28a0833f2126551f
hvm: hpet: Fix overflow when converting to nanoseconds.

Currently in hpet_tick_to_ns, the approach is multiplying first, which
easily causes overflow when tick is quite large. The patch cannot
handle arbitratry large ticks duo to the precision requirement and
64bit's value range. But by optimize the equation, a larger ticks than
current code can be supported. Also an overflow check is added before
the calculation.

From: Haitao Shan <haitao.shan@intel.com>
Signed-off-by: Keir Fraser <keir.fraser@citrix.com>

diff --git a/arch/x86/hvm/hpet.c b/arch/x86/hvm/hpet.c
index 2b8935b..dd05da6 100644
--- a/arch/x86/hvm/hpet.c
+++ b/arch/x86/hvm/hpet.c
@@ -71,8 +71,9 @@
 #define HPET_TN_INT_ROUTE_CAP_MASK (0xffffffffULL \
                     << HPET_TN_INT_ROUTE_CAP_SHIFT)
 
-#define hpet_tick_to_ns(h, tick) ((s_time_t)(tick)* \
-                                  (S_TO_NS*TSC_PER_HPET_TICK)/h->tsc_freq)
+#define hpet_tick_to_ns(h, tick)                        \
+    ((s_time_t)((((tick) > (h)->hpet_to_ns_limit) ?     \
+        ~0ULL : (tick) * (h)->hpet_to_ns_scale) >> 10))
 
 #define timer_config(h, n)       (h->hpet.timers[n].config)
 #define timer_enabled(h, n)      (timer_config(h, n) & HPET_TN_ENABLE)
@@ -467,6 +468,9 @@ void hpet_init(struct vcpu *v)
     h->vcpu = v;
     h->tsc_freq = ticks_per_sec(v);
 
+    h->hpet_to_ns_scale = ((S_TO_NS * TSC_PER_HPET_TICK) << 10) / h->tsc_freq;
+    h->hpet_to_ns_limit = (~0ULL >> 1) / h->hpet_to_ns_scale;
+
     /* 64-bit main counter; 3 timers supported; LegacyReplacementRoute. */
     h->hpet.capability = 0x8086A201ULL;
 
diff --git a/include/asm-x86/hvm/vpt.h b/include/asm-x86/hvm/vpt.h
index 38d4aae..1991f3f 100644
--- a/include/asm-x86/hvm/vpt.h
+++ b/include/asm-x86/hvm/vpt.h
@@ -41,6 +41,8 @@ typedef struct HPETState {
     struct hvm_hw_hpet hpet;
     struct vcpu *vcpu;
     uint64_t tsc_freq;
+    uint64_t hpet_to_ns_scale; /* hpet ticks to ns (multiplied by 2^10) */
+    uint64_t hpet_to_ns_limit; /* max hpet ticks convertable to ns      */
     uint64_t mc_offset;
     struct timer timers[HPET_TIMER_NUM];
     struct HPET_timer_fn_info timer_fn_info[HPET_TIMER_NUM];