On 2012-03-08 22:46, Marcelo Tosatti wrote:
>
> kvm_write_tsc() converts from guest TSC to microseconds, not nanoseconds
> as intended. The result is that the window for matching is 1000 seconds,
> not 1 second.
>
> Microsecond precision is enough for checking whether the TSC write delta
> is within the heuristic values, so use it instead of nanoseconds.
>
> Noted by Avi Kivity.
>
> Signed-off-by: Marcelo Tosatti <mtosa...@redhat.com>
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 32096cf..9732e98 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1025,7 +1025,7 @@ void kvm_write_tsc(struct kvm_vcpu *vcpu, u64 data)
> struct kvm *kvm = vcpu->kvm;
> u64 offset, ns, elapsed;
> unsigned long flags;
> - s64 nsdiff;
> + s64 usdiff;
>
> raw_spin_lock_irqsave(&kvm->arch.tsc_write_lock, flags);
> offset = kvm_x86_ops->compute_tsc_offset(vcpu, data);
> @@ -1033,18 +1033,18 @@ void kvm_write_tsc(struct kvm_vcpu *vcpu, u64 data)
> elapsed = ns - kvm->arch.last_tsc_nsec;
>
> /* n.b - signed multiplication and division required */
> - nsdiff = data - kvm->arch.last_tsc_write;
> + usdiff = data - kvm->arch.last_tsc_write;
> #ifdef CONFIG_X86_64
> - nsdiff = (nsdiff * 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"(nsdiff)
> - : "A"(nsdiff * 1000), "rm"(vcpu->arch.virtual_tsc_khz));
> + : "=A"(usdiff)
> + : "A"(usdiff * 1000), "rm"(vcpu->arch.virtual_tsc_khz));
> #endif
> - nsdiff -= elapsed;
> - if (nsdiff < 0)
> - nsdiff = -nsdiff;
> + usdiff -= elapsed / 1000;
do_div, to please x86-32.
Jan
> + if (usdiff < 0)
> + usdiff = -usdiff;
>
> /*
> * Special case: TSC write with a small delta (1 second) of virtual
> @@ -1056,7 +1056,7 @@ void kvm_write_tsc(struct kvm_vcpu *vcpu, u64 data)
> * compensation code attempt to catch up if we fall behind, but
> * it's better to try to match offsets from the beginning.
> */
> - if (nsdiff < NSEC_PER_SEC &&
> + if (usdiff < USEC_PER_SEC &&
> vcpu->arch.virtual_tsc_khz == kvm->arch.last_tsc_khz) {
> if (!check_tsc_unstable()) {
> offset = kvm->arch.cur_tsc_offset;
> --
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