Re: [PATCH v4 2/2] xen: delay xen_hvm_init_time_ops() if kdump is boot on vcpu>=32

[Boris Ostrovsky]

On 3/2/22 7:31 PM, Dongli Zhang wrote:
> Hi Boris,
>
> On 3/2/22 4:20 PM, Boris Ostrovsky wrote:
> > On 3/2/22 11:40 AM, Dongli Zhang wrote:
> > >    void __init xen_hvm_init_time_ops(void)
> > >    {
> > > +    static bool hvm_time_initialized;
> > > +
> > > +    if (hvm_time_initialized)
> > > +        return;
> > > +
> > >        /*
> > >         * vector callback is needed otherwise we cannot receive interrupts
> > >         * on cpu > 0 and at this point we don't know how many cpus are
> > >         * available.
> > >         */
> > >        if (!xen_have_vector_callback)
> > > -        return;
> > > +        goto exit;
> >
> > Why not just return? Do we expect the value of xen_have_vector_callback to change?
> I just want to keep above sync with ....
>
> > -boris
> >
> >
> > >          if (!xen_feature(XENFEAT_hvm_safe_pvclock)) {
> > >            pr_info("Xen doesn't support pvclock on HVM, disable pv timer");
> > > +        goto exit;
> > > +    }
> ... here.
>
> That is, I want the main logic of xen_hvm_init_time_ops() to run for at most
> once. Both of above two if statements will "go to exit".


I didn't notice this actually.


I think both of them should return early, there is no reason to set hvm_time_initialized to true when, in fact, we have not initialized anything. And to avoid printing the warning twice we can just replace it with pr_info_once().


I can fix it up when committing so no need to resend. So unless you disagree


Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>


> Thank you very much!
>
> Dongli Zhang
>
> > > +
> > > +    /*
> > > +     * Only MAX_VIRT_CPUS 'vcpu_info' are embedded inside 'shared_info'.
> > > +     * The __this_cpu_read(xen_vcpu) is still NULL when Xen HVM guest
> > > +     * boots on vcpu >= MAX_VIRT_CPUS (e.g., kexec), To access
> > > +     * __this_cpu_read(xen_vcpu) via xen_clocksource_read() will panic.
> > > +     *
> > > +     * The xen_hvm_init_time_ops() should be called again later after
> > > +     * __this_cpu_read(xen_vcpu) is available.
> > > +     */
> > > +    if (!__this_cpu_read(xen_vcpu)) {
> > > +        pr_info("Delay xen_init_time_common() as kernel is running on
> > > vcpu=%d\n",
> > > +            xen_vcpu_nr(0));
> > >            return;
> > >        }
> > >    @@ -577,6 +597,9 @@ void __init xen_hvm_init_time_ops(void)
> > >        x86_cpuinit.setup_percpu_clockev = xen_hvm_setup_cpu_clockevents;
> > >          x86_platform.set_wallclock = xen_set_wallclock;
> > > +
> > > +exit:
> > > +    hvm_time_initialized = true;
> > >    }
> > >    #endif
> > >