VMX: x86: handle host TSC calibration failure

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>
Signed-off-by: Gleb Natapov <gleb@redhat.com>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 35b4912..b67985a 100644 (file)
--- 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