From 6443c73ab06239ab4b1bc0511d9b78f7122f477d Mon Sep 17 00:00:00 2001
From: Paolo Bonzini <pbonzini@redhat.com>
Date: Mon, 27 Jun 2016 15:08:01 +0200
Subject: KVM: vmx: fix underflow in TSC deadline calculation
If the TSC deadline timer is programmed really close to the deadline or
even in the past, the computation in vmx_set_hv_timer can underflow and
cause delta_tsc to be set to a huge value. This generally results
in vmx_set_hv_timer returning -ERANGE, but we can fix it by limiting
delta_tsc to be positive or zero.
Reported-by: Wanpeng Li <wanpeng.li@hotmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Change-Id: I12eea18c3ec648dbf782d7754b7b574d7d6aa92c
upstream-status: backport
Signed-off-by: Yunhong Jiang <yunhong.jiang@linux.intel.com>
---
kernel/arch/x86/kvm/vmx.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
(limited to 'kernel')
diff --git a/kernel/arch/x86/kvm/vmx.c b/kernel/arch/x86/kvm/vmx.c
index e378975f5..5da019be6 100644
--- a/kernel/arch/x86/kvm/vmx.c
+++ b/kernel/arch/x86/kvm/vmx.c
@@ -10663,9 +10663,9 @@ static inline int u64_shl_div_u64(u64 a, unsigned int shift,
static int vmx_set_hv_timer(struct kvm_vcpu *vcpu, u64 guest_deadline_tsc)
{
struct vcpu_vmx *vmx = to_vmx(vcpu);
- u64 tscl = rdtsc(), delta_tsc;
-
- delta_tsc = guest_deadline_tsc - kvm_read_l1_tsc(vcpu, tscl);
+ u64 tscl = rdtsc();
+ u64 guest_tscl = kvm_read_l1_tsc(vcpu, tscl);
+ u64 delta_tsc = max(guest_deadline_tsc, guest_tscl) - guest_tscl;
/* Convert to host delta tsc if tsc scaling is enabled */
if (vcpu->arch.tsc_scaling_ratio != kvm_default_tsc_scaling_ratio &&
--
cgit