From 6443c73ab06239ab4b1bc0511d9b78f7122f477d Mon Sep 17 00:00:00 2001 From: Paolo Bonzini 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 Signed-off-by: Paolo Bonzini Change-Id: I12eea18c3ec648dbf782d7754b7b574d7d6aa92c upstream-status: backport Signed-off-by: Yunhong Jiang --- kernel/arch/x86/kvm/vmx.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) 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 1.2.3-korg