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KVM: Use a local struct to do the initial vfs_poll() on an irqfd

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Use a function-local struct for the poll_table passed to vfs_poll(), as
nothing in the vfs_poll() callchain grabs a long-term reference to the
structure, i.e. its lifetime doesn't need to be tied to the irqfd.  Using
a local structure will also allow propagating failures out of the polling
callback without further polluting kvm_kernel_irqfd.

Opportunstically rename irqfd_ptable_queue_proc() to kvm_irqfd_register()
to capture what it actually does.

Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250522235223.3178519-2-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson 2025-05-22 16:52:11 -07:00
parent 6f34372483
commit 283ed5001d
2 changed files with 17 additions and 10 deletions
Download patch file Download diff file Expand all files Collapse all files

1
include/linux/kvm_irqfd.h
View file

@ -55,7 +55,6 @@ struct kvm_kernel_irqfd {
/* Used for setup/shutdown */
struct eventfd_ctx *eventfd;
struct list_head list;
poll_table pt;
struct work_struct shutdown;
struct irq_bypass_consumer consumer;
struct irq_bypass_producer *producer;

26
virt/kvm/eventfd.c
View file

@ -245,12 +245,17 @@ irqfd_wakeup(wait_queue_entry_t *wait, unsigned mode, int sync, void *key)
return ret;
}
static void
irqfd_ptable_queue_proc(struct file *file, wait_queue_head_t *wqh,
poll_table *pt)
struct kvm_irqfd_pt {
struct kvm_kernel_irqfd *irqfd;
poll_table pt;
};
static void kvm_irqfd_register(struct file *file, wait_queue_head_t *wqh,
poll_table *pt)
{
struct kvm_kernel_irqfd *irqfd =
container_of(pt, struct kvm_kernel_irqfd, pt);
struct kvm_irqfd_pt *p = container_of(pt, struct kvm_irqfd_pt, pt);
struct kvm_kernel_irqfd *irqfd = p->irqfd;
add_wait_queue_priority(wqh, &irqfd->wait);
}
@ -298,6 +303,7 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args)
{
struct kvm_kernel_irqfd *irqfd, *tmp;
struct eventfd_ctx *eventfd = NULL, *resamplefd = NULL;
struct kvm_irqfd_pt irqfd_pt;
int ret;
__poll_t events;
int idx;
@ -387,7 +393,6 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args)
* a callback whenever someone signals the underlying eventfd
*/
init_waitqueue_func_entry(&irqfd->wait, irqfd_wakeup);
init_poll_funcptr(&irqfd->pt, irqfd_ptable_queue_proc);
spin_lock_irq(&kvm->irqfds.lock);
@ -409,11 +414,14 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args)
spin_unlock_irq(&kvm->irqfds.lock);
/*
* Check if there was an event already pending on the eventfd
* before we registered, and trigger it as if we didn't miss it.
* Register the irqfd with the eventfd by polling on the eventfd. If
* there was en event pending on the eventfd prior to registering,
* manually trigger IRQ injection.
*/
events = vfs_poll(fd_file(f), &irqfd->pt);
irqfd_pt.irqfd = irqfd;
init_poll_funcptr(&irqfd_pt.pt, kvm_irqfd_register);
events = vfs_poll(fd_file(f), &irqfd_pt.pt);
if (events & EPOLLIN)
schedule_work(&irqfd->inject);