linux-kernel - Re: [PATCH v2] drivers/xen: Improve the late XenStore init protocol

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Date: Thu, 16 May 2024 18:21:55 -0700 (PDT)
From: Stefano Stabellini <sstabellini@...nel.org>
To: Henry Wang <xin.wang2@....com>
cc: xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org, 
    Juergen Gross <jgross@...e.com>, 
    Stefano Stabellini <sstabellini@...nel.org>, 
    Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>, 
    Michal Orzel <michal.orzel@....com>
Subject: Re: [PATCH v2] drivers/xen: Improve the late XenStore init
 protocol

On Fri, 17 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() to select the code path of doing the
> late XenStore init protocol or not. Since now we have more than one
> condition for XenStore late init, rework the check in xenbus_probe()
> for the free_irq().
> 
> Take the opportunity to enhance the check of the allocated XenStore
> interface can be properly mapped, and return error early if the
> memremap() fails.
> 
> Fixes: 5b3353949e89 ("xen: add support for initializing xenstore later as HVM domain")
> Signed-off-by: Henry Wang <xin.wang2@....com>
> Signed-off-by: Michal Orzel <michal.orzel@....com>

Reviewed-by: Stefano Stabellini <sstabellini@...nel.org>


> ---
> v2:
> - Use -EINVAL for the memremap() check. (Stefano)
> - Add Fixes: tag. (Stefano)
> - Rework the condition for free_irq() in xenbus_probe(). (Stefano)
> ---
>  drivers/xen/xenbus/xenbus_probe.c | 36 ++++++++++++++++++++-----------
>  1 file changed, 23 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/xen/xenbus/xenbus_probe.c b/drivers/xen/xenbus/xenbus_probe.c
> index 3205e5d724c8..1a9ded0cddcb 100644
> --- a/drivers/xen/xenbus/xenbus_probe.c
> +++ b/drivers/xen/xenbus/xenbus_probe.c
> @@ -65,13 +65,17 @@
>  #include "xenbus.h"
>  
>  
> -static int xs_init_irq;
> +static int xs_init_irq = -1;
>  int xen_store_evtchn;
>  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);
>  
> @@ -751,19 +755,19 @@ static void xenbus_probe(void)
>  {
>  	xenstored_ready = 1;
>  
> -	if (!xen_store_interface) {
> +	if (!xen_store_interface)
>  		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
> -		 * bound again from xb_init_comms. Note that calling
> -		 * unbind_from_irqhandler now would result in xen_evtchn_close()
> -		 * being called and the event channel not being enabled again
> -		 * afterwards, resulting in missed event notifications.
> -		 */
> +	/*
> +	 * Now it is safe to free the IRQ used for xenstore late
> +	 * initialization. No need to unbind: it is about to be
> +	 * bound again from xb_init_comms. Note that calling
> +	 * unbind_from_irqhandler now would result in xen_evtchn_close()
> +	 * being called and the event channel not being enabled again
> +	 * afterwards, resulting in missed event notifications.
> +	 */
> +	if (xs_init_irq >= 0)
>  		free_irq(xs_init_irq, &xb_waitq);
> -	}
>  
>  	/*
>  	 * In the HVM case, xenbus_init() deferred its call to
> @@ -822,7 +826,7 @@ 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 +835,7 @@ 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 +1018,12 @@ 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 = -EINVAL;
> +				goto out_error;
> +			}
>  			if (xen_store_interface->connection != XENSTORE_CONNECTED)
>  				wait = true;
>  		}
> -- 
> 2.34.1
>