Il 19/08/2014 22:35, Radim Krčmář ha scritto:
> Every increase of ple_window_grow creates potential overflows.
> They are not serious, because we clamp ple_window and userspace is
> expected to fix ple_window_max within a second.
> ---
> arch/x86/kvm/vmx.c | 34 +++++++++++++++++++++++++++++++++-
> 1 file changed, 33 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index d7f58e8..6873a0b 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -138,7 +138,9 @@ module_param(ple_window, int, S_IRUGO | S_IWUSR);
>
> /* Default doubles per-vcpu window every exit. */
> static int ple_window_grow = KVM_VMX_DEFAULT_PLE_WINDOW_GROW;
> -module_param(ple_window_grow, int, S_IRUGO | S_IWUSR);
> +static struct kernel_param_ops ple_window_grow_ops;
> +module_param_cb(ple_window_grow, &ple_window_grow_ops,
> + &ple_window_grow, S_IRUGO | S_IWUSR);
>
> /* Default resets per-vcpu window every exit to ple_window. */
> static int ple_window_shrink = KVM_VMX_DEFAULT_PLE_WINDOW_SHRINK;
> @@ -5717,6 +5719,36 @@ static void type##_ple_window(struct kvm_vcpu *vcpu) \
> make_ple_window_modifier(grow, *, +) /* grow_ple_window */
> make_ple_window_modifier(shrink, /, -) /* shrink_ple_window */
>
> +static void clamp_ple_window_max(void)
> +{
> + int maximum;
> +
> + if (ple_window_grow < 1)
> + return;
> +
> + if (ple_window_grow < ple_window)
> + maximum = INT_MAX / ple_window_grow;
> + else
> + maximum = INT_MAX - ple_window_grow;
> +
> + ple_window_max = clamp(ple_window_max, ple_window, maximum);
> +}
I think avoiding overflows is better. In fact, I think you should call
this function for ple_window_max too.
You could keep the ple_window_max variable to the user-set value.
Whenever ple_window_grow or ple_window_max are changed, you can set an
internal variable (let's call it ple_window_actual_max, but I'm not wed
to this name) to the computed value, and then do:
if (ple_window_grow < 1 || ple_window_actual_max < ple_window)
new = ple_window;
else if (ple_window_grow < ple_window)
new = max(ple_window_actual_max, old) * ple_window_grow;
else
new = max(ple_window_actual_max, old) + ple_window_grow;
(I think the || in the first "if" can be eliminated with some creativity
in clamp_ple_window_max).
Paolo
> +static int set_ple_window_grow(const char *arg, const struct kernel_param *kp)
> +{
> + int ret;
> +
> + clamp_ple_window_max();
> + ret = param_set_int(arg, kp);
> +
> + return ret;
> +}
> +
> +static struct kernel_param_ops ple_window_grow_ops = {
> + .set = set_ple_window_grow,
> + .get = param_get_int,
> +};
> +
> /*
> * Indicate a busy-waiting vcpu in spinlock. We do not enable the PAUSE
> * exiting, so only get here on cpu with PAUSE-Loop-Exiting.
>
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
