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SubjectRe: [PATCH] drivers/xen: Improve the late XenStore init protocol
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@amd.com>
> Signed-off-by: Michal Orzel <michal.orzel@amd.com>

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
>

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