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Re: [PATCH v6 18/23] xen/riscv: implement IRQ routing for device passthrough
On 7/30/26 9:18 AM, Jan Beulich wrote:
On 29.07.2026 17:23, Oleksii Kurochko wrote:
On 7/29/26 5:02 PM, Oleksii Kurochko wrote:
On 7/29/26 4:15 PM, Jan Beulich wrote:
On 29.07.2026 13:59, Oleksii Kurochko wrote:
On 7/23/26 3:30 PM, Jan Beulich wrote:
On 20.07.2026 17:59, Oleksii Kurochko wrote:
+/* Route an IRQ to a specific guest */
+int route_irq_to_guest(struct domain *d, unsigned int virq,
+ unsigned int irq, const char *devname)
+{
+ struct irqaction *action;
+ struct irq_guest *info;
+ struct irq_desc *desc;
+ unsigned long flags;
+ int retval = 0;
+
+ if ( d->is_dying )
+ return -EINVAL;
+
+ desc = irq_to_desc(irq);
+
+ /*
+ * release_irq() frees this action via xvfree(), relying on
action
+ * being the first member of struct irq_guest so that &info-
action
+ * coincides with info itself. Guard the layout so a future field
+ * reorder can't silently turn that into a free() of a mid-
allocation
+ * pointer.
+ */
+ BUILD_BUG_ON(offsetof(struct irq_guest, action) != 0);
Can't release_irq() simply use container_of()? One way or another it
feels
like you're painting yourself into a particular corner ...
If it isn't the best option then it is needed to follow they way we had
before:
I don't understand why you think you need to go back.
Because, based on your reply—specifically, "One way or another it feels
like you're painting yourself into a particular corner..." — it seems
that even if I replaced BUILD_BUG_ON() with container_of() in
release_irq(), you would still consider it a bad solution. Did I
misunderstand your point?
One more thing: I'm not really sure it's safe to do the following in
release_irq():
if ( action->free_on_release )
xvfree(container_of(action, struct irq_guest, action));
release_irq() is a generic API, but this kind of allocation is only
needed for guest IRQs. Wouldn't it be better to set:
action->free_on_release = false;
for guest IRQs, and then free the memory in release_guest_irq() after
the call to release_irq()?
Perhaps.
Wouldn't that be a better approach than calling
`xvfree(container_of(...))` from within the generic release_irq()?
Perhaps.
What I'd really like to see you do is come up with an approach that is
both self-consistent and future-proof. With the latter aspect meaning that
it should be (reasonably) easy to identify places that need changing if
e.g. the "->free_on_release is only ever one value" property goes away.
An approach with action->free_on_release = false; together with
vfree(info) in release_guest_irq() seems to be the best option. Since
action is no longer allocated dynamically, it should not be freed
through free_on_release, so setting it to false makes that explicit.
Additionally, guest IRQs have extra state (struct irq_guest), and it is
the responsibility of release_guest_irq() to clean it up.
This also keeps the semantics of ->free_on_release consistent for Xen
IRQs. If it is set to true, release_irq() is responsible for freeing
struct irq_action; if it is false, release_irq() should not free it.
For guest interrupts, release_irq() should not free anything because
struct irq_action is embedded in struct irq_guest, which is freed by
release_guest_irq(). If, in the future, guest interrupts need
->free_on_release = true, the only required change would be to allocate
struct irq_action dynamically and set ->free_on_release = true. All
other is already covered. That makes the design, in my opinion,
self-consistent and future-proof.
~ Oleksii
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