Re: [PATCH] drivers/xen: Improve the late XenStore init protocol

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Wed, 15 May 2024, Henry Wang wrote:
> Currently, the late XenStore init protocol is only triggered properly
> for the case that HVM_PARAM_STORE_PFN is ~0ULL (invalid). For the
> case that XenStore interface is allocated but not ready (the connection
> status is not XENSTORE_CONNECTED), Linux should also wait until the
> XenStore is set up properly.
> 
> Introduce a macro to describe the XenStore interface is ready, use
> it in xenbus_probe_initcall() and xenbus_probe() to select the code
> path of doing the late XenStore init protocol or not.
> 
> Take the opportunity to enhance the check of the allocated XenStore
> interface can be properly mapped, and return error early if the
> memremap() fails.
> 
> Signed-off-by: Henry Wang <xin.wang2@xxxxxxx>
> Signed-off-by: Michal Orzel <michal.orzel@xxxxxxx>

Please add a Fixes: tag


> ---
>  drivers/xen/xenbus/xenbus_probe.c | 21 ++++++++++++++++-----
>  1 file changed, 16 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/xen/xenbus/xenbus_probe.c 
> b/drivers/xen/xenbus/xenbus_probe.c
> index 3205e5d724c8..8aec0ed1d047 100644
> --- a/drivers/xen/xenbus/xenbus_probe.c
> +++ b/drivers/xen/xenbus/xenbus_probe.c
> @@ -72,6 +72,10 @@ EXPORT_SYMBOL_GPL(xen_store_evtchn);
>  struct xenstore_domain_interface *xen_store_interface;
>  EXPORT_SYMBOL_GPL(xen_store_interface);
>  
> +#define XS_INTERFACE_READY \
> +     ((xen_store_interface != NULL) && \
> +      (xen_store_interface->connection == XENSTORE_CONNECTED))
> +
>  enum xenstore_init xen_store_domain_type;
>  EXPORT_SYMBOL_GPL(xen_store_domain_type);
>  
> @@ -751,9 +755,10 @@ static void xenbus_probe(void)
>  {
>       xenstored_ready = 1;
>  
> -     if (!xen_store_interface) {
> -             xen_store_interface = memremap(xen_store_gfn << XEN_PAGE_SHIFT,
> -                                            XEN_PAGE_SIZE, MEMREMAP_WB);
> +     if (!xen_store_interface || XS_INTERFACE_READY) {
> +             if (!xen_store_interface)

These two nested if's don't make sense to me. If XS_INTERFACE_READY
succeeds, it means that  ((xen_store_interface != NULL) &&
(xen_store_interface->connection == XENSTORE_CONNECTED)).

So it is not possible that xen_store_interface == NULL immediately
after. Right?


> +                     xen_store_interface = memremap(xen_store_gfn << 
> XEN_PAGE_SHIFT,
> +                                                    XEN_PAGE_SIZE, 
> MEMREMAP_WB);
>               /*
>                * Now it is safe to free the IRQ used for xenstore late
>                * initialization. No need to unbind: it is about to be
> @@ -822,7 +827,7 @@ static int __init xenbus_probe_initcall(void)
>       if (xen_store_domain_type == XS_PV ||
>           (xen_store_domain_type == XS_HVM &&
>            !xs_hvm_defer_init_for_callback() &&
> -          xen_store_interface != NULL))
> +          XS_INTERFACE_READY))
>               xenbus_probe();
>  
>       /*
> @@ -831,7 +836,7 @@ static int __init xenbus_probe_initcall(void)
>        * started, then probe.  It will be triggered when communication
>        * starts happening, by waiting on xb_waitq.
>        */
> -     if (xen_store_domain_type == XS_LOCAL || xen_store_interface == NULL) {
> +     if (xen_store_domain_type == XS_LOCAL || !XS_INTERFACE_READY) {
>               struct task_struct *probe_task;
>  
>               probe_task = kthread_run(xenbus_probe_thread, NULL,
> @@ -1014,6 +1019,12 @@ static int __init xenbus_init(void)
>                       xen_store_interface =
>                               memremap(xen_store_gfn << XEN_PAGE_SHIFT,
>                                        XEN_PAGE_SIZE, MEMREMAP_WB);
> +                     if (!xen_store_interface) {
> +                             pr_err("%s: cannot map 
> HVM_PARAM_STORE_PFN=%llx\n",
> +                                    __func__, v);
> +                             err = -ENOMEM;

I think this should -EINVAL


> +                             goto out_error;
> +                     }
>                       if (xen_store_interface->connection != 
> XENSTORE_CONNECTED)
>                               wait = true;
>               }
> -- 
> 2.34.1
>