VMX: x86: handle host TSC calibration failure

Marcelo Tosatti
2013-03-12T02:10:33Z

If the host TSC calibration fails, tsc_khz is zero (see tsc_init.c).
Handle such case properly in KVM (instead of dividing by zero).

https://bugzilla.redhat.com/show_bug.cgi?id=859282

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 35b4912..19741b9 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1079,6 +1079,10 @@ static void kvm_set_tsc_khz(struct kvm_vcpu *vcpu, u32 this_tsc_khz)
u32 thresh_lo, thresh_hi;
int use_scaling = 0;

+ /* tsc_khz can be zero if TSC calibration fails */
+ if (this_tsc_khz == 0)
+ return;
+
/* Compute a scale to convert nanoseconds in TSC cycles */
kvm_get_time_scale(this_tsc_khz, NSEC_PER_SEC / 1000,
&vcpu->arch.virtual_tsc_shift,
@@ -1156,20 +1160,23 @@ void kvm_write_tsc(struct kvm_vcpu *vcpu, struct msr_data *msr)
ns = get_kernel_ns();
elapsed = ns - kvm->arch.last_tsc_nsec;

- /* n.b - signed multiplication and division required */
- usdiff = data - kvm->arch.last_tsc_write;
+ if (vcpu->arch.virtual_tsc_khz) {
+ /* n.b - signed multiplication and division required */
+ usdiff = data - kvm->arch.last_tsc_write;
#ifdef CONFIG_X86_64
- usdiff = (usdiff * 1000) / vcpu->arch.virtual_tsc_khz;
+ usdiff = (usdiff * 1000) / vcpu->arch.virtual_tsc_khz;
#else
- /* do_div() only does unsigned */
- asm("idivl %2; xor %%edx, %%edx"
- : "=A"(usdiff)
- : "A"(usdiff * 1000), "rm"(vcpu->arch.virtual_tsc_khz));
+ /* do_div() only does unsigned */
+ asm("idivl %2; xor %%edx, %%edx"
+ : "=A"(usdiff)
+ : "A"(usdiff * 1000), "rm"(vcpu->arch.virtual_tsc_khz));
#endif
- do_div(elapsed, 1000);
- usdiff -= elapsed;
- if (usdiff < 0)
- usdiff = -usdiff;
+ do_div(elapsed, 1000);
+ usdiff -= elapsed;
+ if (usdiff < 0)
+ usdiff = -usdiff;
+ } else
+ usdiff = USEC_PER_SEC; /* disable TSC match window below */

/*
* Special case: TSC write with a small delta (1 second) of virtual