[v3,3/7] xen: add a domain unique id to each domain

Commit Message

Jürgen Groß Dec. 13, 2024, 4:24 p.m. UTC

Xenstore is referencing domains by their domid, but reuse of a domid
can lead to the situation that Xenstore can't tell whether a domain
with that domid has been deleted and created again without Xenstore
noticing the domain is a new one now.

Add a global domain creation unique id which is updated when creating
a new domain, and store that value in struct domain of the new domain.
The global unique id is initialized with the system time and updates
are done via the xorshift algorithm which is used for pseudo random
number generation, too (see https://en.wikipedia.org/wiki/Xorshift).

Signed-off-by: Juergen Gross <[e-mail]>
Reviewed-by: Jan Beulich <[e-mail]>
Reviewed-by: Alejandro Vallejo <[e-mail]>
---
V1:
- make unique_id local to function (Jan Beulich)
- add lock (Julien Grall)
- add comment (Julien Grall)
V2:
- move reading unique_id into locked section (Julien Grall)
- add comment (Alejandro Vallejo)
---
 xen/common/domain.c     | 27 +++++++++++++++++++++++++++
 xen/include/xen/sched.h |  3 +++
 2 files changed, 30 insertions(+)

Patch

diff --git a/xen/common/domain.c b/xen/common/domain.c
index 92263a4fbd..e33a0a5a21 100644
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -562,6 +562,32 @@  static void _domain_destroy(struct domain *d)
     free_domain_struct(d);
 }
 
+static uint64_t get_unique_id(void)
+{
+    static uint64_t unique_id;
+    static DEFINE_SPINLOCK(lock);
+    uint64_t x;
+
+    spin_lock(&lock);
+
+    x = unique_id ? : NOW();
+
+    /*
+     * Pseudo-randomize id in order to avoid consumers relying on sequence.
+     * Randomization algorithm has a period of 2^64 - 1.
+     * Unique id is not repeatable between resets and each id has the same
+     * lifetime as the domain it is associated with.
+     */
+    x ^= x << 13;
+    x ^= x >> 7;
+    x ^= x << 17;
+    unique_id = x;
+
+    spin_unlock(&lock);
+
+    return x;
+}
+
 static int sanitise_domain_config(struct xen_domctl_createdomain *config)
 {
     bool hvm = config->flags & XEN_DOMCTL_CDF_hvm;
@@ -654,6 +680,7 @@  struct domain *domain_create(domid_t domid,
 
     /* Sort out our idea of is_system_domain(). */
     d->domain_id = domid;
+    d->unique_id = get_unique_id();
 
     /* Holding CDF_* internal flags. */
     d->cdf = flags;
diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
index 76e39378b3..711668e028 100644
--- a/xen/include/xen/sched.h
+++ b/xen/include/xen/sched.h
@@ -370,6 +370,9 @@  struct domain
     domid_t          domain_id;
 
     unsigned int     max_vcpus;
+
+    uint64_t         unique_id;       /* Unique domain identifier */
+
     struct vcpu    **vcpu;
 
     shared_info_t   *shared_info;     /* shared data area */