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[Xen-devel] [PATCH] x86: fix delta calculation in TSC deadline timer emulation

From: David Vrabel <david.vrabel@xxxxxxxxxx>

In the virtual LAPIC, correct the delta calculation when emulating the
TSC deadline timer.

Without this fix, XenServer (which is based on Xen 4.1) does not work
when running as an HVM guest.  dom0 fails to boot because its timer
interrupts are very delayed (by several minutes in some cases).

Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
Cc: Keir Fraser <keir@xxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
A 4.1.x candidate?
 xen/arch/x86/hvm/vlapic.c |    5 ++---
 1 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/xen/arch/x86/hvm/vlapic.c b/xen/arch/x86/hvm/vlapic.c
index 8401756..1aa2810 100644
--- a/xen/arch/x86/hvm/vlapic.c
+++ b/xen/arch/x86/hvm/vlapic.c
@@ -913,9 +913,8 @@ void vlapic_tdt_msr_set(struct vlapic *vlapic, uint64_t 
     guest_time = hvm_get_guest_time(v);
     if ( value > guest_tsc )
-        uint64_t delta = value - v->arch.hvm_vcpu.cache_tsc_offset;
-        delta = gtsc_to_gtime(v->domain, delta);
-        delta = max_t(s64, delta - guest_time, 0);
+        uint64_t delta = gtsc_to_gtime(v->domain, value - guest_tsc);
+        delta = max_t(s64, delta, 0);
         HVM_DBG_LOG(DBG_LEVEL_VLAPIC_TIMER, "delta[0x%016"PRIx64"]", delta);

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