@samitouri / QOSamiQemu / commits / 0f53f021ad

accel/kvm: notify when KVM VM file fd is about to be changed

Various subsystems might need to take some steps before the KVM file descriptor for a virtual machine is changed. So a new boolean attribute is added to the vmfd_notifier structure which is passed to the notifier callbacks. vmfd_notifer.pre is true for pre-notification of vmfd change and false for post notification. Notifier callback implementations can simply check the boolean value for (vmfd_notifer*)->pre and can take actions for pre or post vmfd change based on the value. Subsequent patches will add callback implementations for specific components that need this pre-notification. Signed-off-by: Ani Sinha <anisinha@redhat.com> Link: https://lore.kernel.org/r/20260225035000.385950-9-anisinha@redhat.com Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Ani Sinha committed Feb 25, 2026 at 09:19 UTC 0f53f021ad1ede28dc8944686544e496cab02e5e

2 files changed +13 -2

accel/kvm/kvm-all.c

@@ -2654,6 +2654,13 @@ static int kvm_reset_vmfd(MachineState *ms)

2654 memory_listener_unregister(&kml->listener);

2655 memory_listener_unregister(&kvm_io_listener);

2656

2657 + vmfd_notifier.pre = true;

2658 + ret = kvm_vmfd_change_notify(&err);

2659 + if (ret < 0) {

2660 + return ret;

2661 + }

2662 + assert(!err);

2663 +

2664 if (s->vmfd >= 0) {

2665 close(s->vmfd);

2666 }

@@ -2695,6 +2702,8 @@ static int kvm_reset_vmfd(MachineState *ms)

2702 * notify everyone that vmfd has changed.

2703 */

2704 vmfd_notifier.vmfd = s->vmfd;

2705 + vmfd_notifier.pre = false;

2706 +

2707 ret = kvm_vmfd_change_notify(&err);

2708 if (ret < 0) {

2709 return ret;

include/system/kvm.h

+4 -2

@@ -571,12 +571,14 @@ int kvm_convert_memory(hwaddr start, hwaddr size, bool to_private);

571 /* argument to vmfd change notifier */

572 typedef struct VmfdChangeNotifier {

573 int vmfd;

574 + bool pre;

575 } VmfdChangeNotifier;

576

577 /**

578 * kvm_vmfd_add_change_notifier - register a notifier to get notified when

578 - * a KVM vm file descriptor changes as a part of the confidential guest "reset"

579 - * process. Various subsystems should use this mechanism to take actions such

579 + * a KVM vm file descriptor changes or about to be changed as a part of the

580 + * confidential guest "reset" process.

581 + * Various subsystems should use this mechanism to take actions such

582 * as creating new fds against this new vm file descriptor.

583 * @n: notifier with return value.

584 */