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@@ -, +, @@
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VMX: x86: handle host TSC calibration failure
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If the host TSC calibration fails, tsc_khz is zero (see tsc_init.c).
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Handle such case properly in KVM (instead of dividing by zero).
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https://bugzilla.redhat.com/show_bug.cgi?id=859282
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Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
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Signed-off-by: Gleb Natapov <gleb@redhat.com>
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--- a/arch/x86/kvm/x86.c
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+++ a/arch/x86/kvm/x86.c
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@@ -1079,6 +1079,10 @@ static void kvm_set_tsc_khz(struct kvm_vcpu *vcpu, u32 this_tsc_khz)
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u32 thresh_lo, thresh_hi;
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int use_scaling = 0;
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+ /* tsc_khz can be zero if TSC calibration fails */
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+ if (this_tsc_khz == 0)
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+ return;
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+
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/* Compute a scale to convert nanoseconds in TSC cycles */
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kvm_get_time_scale(this_tsc_khz, NSEC_PER_SEC / 1000,
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&vcpu->arch.virtual_tsc_shift,
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@@ -1156,20 +1160,23 @@ void kvm_write_tsc(struct kvm_vcpu *vcpu, struct msr_data *msr)
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ns = get_kernel_ns();
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elapsed = ns - kvm->arch.last_tsc_nsec;
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- /* n.b - signed multiplication and division required */
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- usdiff = data - kvm->arch.last_tsc_write;
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+ if (vcpu->arch.virtual_tsc_khz) {
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+ /* n.b - signed multiplication and division required */
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+ usdiff = data - kvm->arch.last_tsc_write;
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#ifdef CONFIG_X86_64
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- usdiff = (usdiff * 1000) / vcpu->arch.virtual_tsc_khz;
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+ usdiff = (usdiff * 1000) / vcpu->arch.virtual_tsc_khz;
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#else
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- /* do_div() only does unsigned */
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- asm("idivl %2; xor %%edx, %%edx"
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- : "=A"(usdiff)
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- : "A"(usdiff * 1000), "rm"(vcpu->arch.virtual_tsc_khz));
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+ /* do_div() only does unsigned */
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+ asm("idivl %2; xor %%edx, %%edx"
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+ : "=A"(usdiff)
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+ : "A"(usdiff * 1000), "rm"(vcpu->arch.virtual_tsc_khz));
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#endif
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- do_div(elapsed, 1000);
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- usdiff -= elapsed;
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- if (usdiff < 0)
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- usdiff = -usdiff;
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+ do_div(elapsed, 1000);
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+ usdiff -= elapsed;
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+ if (usdiff < 0)
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+ usdiff = -usdiff;
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+ } else
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+ usdiff = USEC_PER_SEC; /* disable TSC match window below */
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/*
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* Special case: TSC write with a small delta (1 second) of virtual
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