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Commit 9175d2e9 authored by Paolo Bonzini's avatar Paolo Bonzini
Browse files

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: default avatarWanpeng Li <wanpeng.li@hotmail.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent f2485b3e

arch/x86/kvm/vmx.c

+3 −3
Original line number Diff line number Diff line
@@ -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 &&