Re: [PATCH v6 4/7] xen: add bitmap to indicate per-domain state changes

[Jürgen Groß]

On 07.01.25 17:14, Jan Beulich wrote:

On 07.01.2025 11:17, Juergen Gross wrote:

Add a bitmap with one bit per possible domid indicating the respective
domain has changed its state (created, deleted, dying, crashed,
shutdown).

Registering the VIRQ_DOM_EXC event will result in setting the bits for
all existing domains and resetting all other bits.

As the usage of this bitmap is tightly coupled with the VIRQ_DOM_EXC
event, it is meant to be used only by a single consumer in the system,
just like the VIRQ_DOM_EXC event.

Resetting a bit will be done in a future patch.

This information is needed for Xenstore to keep track of all domains.

Signed-off-by: Juergen Gross <jgr...@suse.com>
---
V2:
- use DOMID_FIRST_RESERVED instead of DOMID_MASK + 1 (Jan Beulich)
- use const (Jan Beulich)
- move call of domain_reset_states() into evtchn_bind_virq() (Jan Beulich)
- dynamically allocate dom_state_changed bitmap (Jan Beulich)
V3:
- use xvzalloc_array() (Jan Beulich)
- don't rename existing label (Jan Beulich)
V4:
- add __read_mostly (Jan Beulich)
- use __set_bit() (Jan Beulich)

This change looks to have been lost, ...

- fix error handling in evtchn_bind_virq() (Jan Beulich)
V5:
- domain_init_states() may be called only if evtchn_bind_virq() has been
   called validly (Jan Beulich)
V6:
- guard dom_state_changed bitmap with d->event_lock (Jan Beulich)

... without it being mentioned anywhere, and without it becoming clear why
it would have needed undoing.

Oh, thanks for spotting. I changed that by accident and missed to undo
this change.

--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -35,6 +35,7 @@
  #include <xen/irq.h>
  #include <xen/argo.h>
  #include <xen/llc-coloring.h>
+#include <xen/xvmalloc.h>
  #include <asm/p2m.h>
  #include <asm/processor.h>
  #include <public/sched.h>
@@ -139,6 +140,51 @@ bool __read_mostly vmtrace_available;

+
+int domain_init_states(void)
+{
+    const struct domain *d;
+
+    ASSERT(!dom_state_changed);
+    ASSERT(rw_is_write_locked(&current->domain->event_lock));

bool __read_mostly vpmu_is_available; +static unsigned long *__read_mostly dom_state_changed;

rw_is_write_locked_by_me()?

Yes, probably better.

+    dom_state_changed = xvzalloc_array(unsigned long,
+                                       BITS_TO_LONGS(DOMID_FIRST_RESERVED));
+    if ( !dom_state_changed )
+        return -ENOMEM;
+
+    rcu_read_lock(&domlist_read_lock);
+
+    for_each_domain ( d )
+        set_bit(d->domain_id, dom_state_changed);
+
+    rcu_read_unlock(&domlist_read_lock);
+
+    return 0;
+}
+
+void domain_deinit_states(const struct domain *d)
+{
+    ASSERT(rw_is_write_locked(&d->event_lock));

Again.

Yes.


Juergen

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