Re: [LINUX PATCH v2 1/1] xen: add support for initializing xenstore later as HVM domain

[Juergen Gross <jgross@xxxxxxxx>]

On 13.01.22 02:00, Stefano Stabellini wrote:
> From: Luca Miccio <lucmiccio@xxxxxxxxx>
>
> When running as dom0less guest (HVM domain on ARM) the xenstore event
> channel is available at domain creation but the shared xenstore
> interface page only becomes available later on.
>
> In that case, wait for a notification on the xenstore event channel,
> then complete the xenstore initialization later, when the shared page
> is actually available.
>
> Signed-off-by: Luca Miccio <lucmiccio@xxxxxxxxx>
> Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx>
> ---
> Changes in v2:
> - remove XENFEAT_xenstore_late_init
> ---
>   drivers/xen/xenbus/xenbus_probe.c | 80 +++++++++++++++++++++++--------
>   1 file changed, 61 insertions(+), 19 deletions(-)
>
> diff --git a/drivers/xen/xenbus/xenbus_probe.c 
> b/drivers/xen/xenbus/xenbus_probe.c
> index fe360c33ce71..51e52e175892 100644
> --- a/drivers/xen/xenbus/xenbus_probe.c
> +++ b/drivers/xen/xenbus/xenbus_probe.c
> @@ -65,6 +65,7 @@
>   #include "xenbus.h"
>   
>   
> +static int xs_init_irq;
>   int xen_store_evtchn;
>   EXPORT_SYMBOL_GPL(xen_store_evtchn);
>   
> @@ -750,6 +751,17 @@ static void xenbus_probe(void)
>   {
>         xenstored_ready = 1;
>   
> +	if (!xen_store_interface) {
> +               xen_store_interface = xen_remap(xen_store_gfn << XEN_PAGE_SHIFT,
> +                                               XEN_PAGE_SIZE);
> +               /*
> +                * Now it is safe to free the IRQ used for xenstore late
> +                * initialization. No need to unbind: it is about to be
> +                * bound again.
> +                */
> +               free_irq(xs_init_irq, &xb_waitq);
> +       }
> +
>         /*
>          * In the HVM case, xenbus_init() deferred its call to
>          * xs_init() in case callbacks were not operational yet.
> @@ -798,20 +810,22 @@ static int __init xenbus_probe_initcall(void)
>   {
>         /*
>          * Probe XenBus here in the XS_PV case, and also XS_HVM unless we
> -        * need to wait for the platform PCI device to come up.
> +        * need to wait for the platform PCI device to come up or
> +        * xen_store_interface is not ready.
>          */
>         if (xen_store_domain_type == XS_PV ||
>             (xen_store_domain_type == XS_HVM &&
> -            !xs_hvm_defer_init_for_callback()))
> +            !xs_hvm_defer_init_for_callback() &&
> +            xen_store_interface != NULL))
>                 xenbus_probe();
>   
>   	/*
> -        * For XS_LOCAL, spawn a thread which will wait for xenstored
> -        * or a xenstore-stubdom to be started, then probe. It will be
> -        * triggered when communication starts happening, by waiting
> -        * on xb_waitq.
> +        * For XS_LOCAL or when xen_store_interface is not ready, spawn a
> +        * thread which will wait for xenstored or a xenstore-stubdom to be
> +        * started, then probe.  It will be triggered when communication
> +        * starts happening, by waiting on xb_waitq.
>          */
> -       if (xen_store_domain_type == XS_LOCAL) {
> +       if (xen_store_domain_type == XS_LOCAL || xen_store_interface == NULL) {
>                 struct task_struct *probe_task;
>   
>   		probe_task = kthread_run(xenbus_probe_thread, NULL,
> @@ -907,6 +921,20 @@ static struct notifier_block xenbus_resume_nb = {
>         .notifier_call = xenbus_resume_cb,
>   };
>   
> +static irqreturn_t xenbus_late_init(int irq, void *unused)
> +{
> +       int err = 0;
> +       uint64_t v = 0;
> +
> +       err = hvm_get_parameter(HVM_PARAM_STORE_PFN, &v);
> +       if (err || !v || !~v)
> +               return IRQ_HANDLED;
> +       xen_store_gfn = (unsigned long)v;
> +
> +       wake_up(&xb_waitq);
> +       return IRQ_HANDLED;
> +}
> +
Hmm, wouldn't it be easier to use a static key in the already existing
irq handler instead of switching the handler?


Juergen

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