On 5/23/2025 8:03 PM, Sean Christopherson wrote:
On Fri, May 23, 2025, Sairaj Kodilkar wrote:
On 5/23/2025 5:22 AM, Sean Christopherson wrote:
+
+int main(int argc, char *argv[])
+{
+ pthread_t racing_thread;
+ int r, i;
+
+ /* Create "full" VMs, as KVM_IRQFD requires an in-kernel IRQ chip. */
+ vm1 = vm_create(1);
+ vm2 = vm_create(1);
+
+ WRITE_ONCE(__eventfd, kvm_new_eventfd());
+
+ kvm_irqfd(vm1, 10, __eventfd, 0);
+
+ r = __kvm_irqfd(vm1, 11, __eventfd, 0);
+ TEST_ASSERT(r && errno == EBUSY,
+ "Wanted EBUSY, r = %d, errno = %d", r, errno);
+
+ r = __kvm_irqfd(vm2, 12, __eventfd, 0);
+ TEST_ASSERT(r && errno == EBUSY,
+ "Wanted EBUSY, r = %d, errno = %d", r, errno);
+
+ kvm_irqfd(vm1, 11, READ_ONCE(__eventfd), KVM_IRQFD_FLAG_DEASSIGN);
+ kvm_irqfd(vm1, 12, READ_ONCE(__eventfd), KVM_IRQFD_FLAG_DEASSIGN);
+ kvm_irqfd(vm1, 13, READ_ONCE(__eventfd), KVM_IRQFD_FLAG_DEASSIGN);
+ kvm_irqfd(vm1, 14, READ_ONCE(__eventfd), KVM_IRQFD_FLAG_DEASSIGN);
Hi Sean,
I dont see any allocation for the GSI 13 and 14..
Is there any reason for the deassigning these two GSIs ?
Yes, KVM's rather bizarre ABI is that DEASSIGN is allowed even if the VM doesn't
have a corresponding assigned irqfd. The reason I added these early DEASSIGN
calls is so that there will be an easier-to-debug failure if KVM's behavior
changes (the racing threads part of the test abuses KVM's ABI). I didn't add a
comment because the helpers already have comments, but looking at this again, I
agree that main() needs a better comment.
Makes sense, thanks for the explanation.
Thanks
Sairaj Kodilkar
