Messages in this thread | | | Subject | Re: [PATCH] KVM: vmx: fix underflow in TSC deadline calculation | From | Paolo Bonzini <> | Date | Tue, 28 Jun 2016 10:43:13 +0200 |
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On 28/06/2016 08:15, Wanpeng Li wrote: > 2016-06-27 21:11 GMT+08:00 Paolo Bonzini <pbonzini@redhat.com>: >> 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> >> --- >> arch/x86/kvm/vmx.c | 6 +++--- >> 1 file changed, 3 insertions(+), 3 deletions(-) >> >> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c >> index c1d655c10fd2..85e2f0a882ca 100644 >> --- a/arch/x86/kvm/vmx.c >> +++ b/arch/x86/kvm/vmx.c >> @@ -10829,9 +10829,9 @@ 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 && > > This patch still can't fix the bug after my testing. I have a patch on > hand and will send out soon.
Nice! Do you think we need both patches?
Thanks,
Paolo
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