Re: [PATCH V5 20/38] migration: close kvm after cpr

[Steven Sistare <steven.sistare@oracle.com>]

Hi Paolo, Peter, Fabiano,

This patch needs review.  CPR for vfio is broken without it.
Soft feature freeze July 15.

- Steve

On 6/10/2025 11:39 AM, Steve Sistare wrote:
> cpr-transfer breaks vfio network connectivity to and from the guest, and
> the host system log shows:
>    irq bypass consumer (token 00000000a03c32e5) registration fails: -16
> which is EBUSY.  This occurs because KVM descriptors are still open in
> the old QEMU process.  Close them.
> 
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
> ---
>   include/hw/vfio/vfio-device.h |  2 ++
>   include/migration/cpr.h       |  2 ++
>   include/system/kvm.h          |  1 +
>   accel/kvm/kvm-all.c           | 32 ++++++++++++++++++++++++++++++++
>   accel/stubs/kvm-stub.c        |  5 +++++
>   hw/vfio/helpers.c             | 10 ++++++++++
>   hw/vfio/vfio-stubs.c          | 13 +++++++++++++
>   migration/cpr-transfer.c      | 18 ++++++++++++++++++
>   migration/cpr.c               |  8 ++++++++
>   migration/migration.c         |  1 +
>   hw/vfio/meson.build           |  2 ++
>   11 files changed, 94 insertions(+)
>   create mode 100644 hw/vfio/vfio-stubs.c
> 
> diff --git a/include/hw/vfio/vfio-device.h b/include/hw/vfio/vfio-device.h
> index 4e4d0b6..6eb6f21 100644
> --- a/include/hw/vfio/vfio-device.h
> +++ b/include/hw/vfio/vfio-device.h
> @@ -231,4 +231,6 @@ void vfio_device_set_fd(VFIODevice *vbasedev, const char *str, Error **errp);
>   void vfio_device_init(VFIODevice *vbasedev, int type, VFIODeviceOps *ops,
>                         DeviceState *dev, bool ram_discard);
>   int vfio_device_get_aw_bits(VFIODevice *vdev);
> +
> +void vfio_kvm_device_close(void);
>   #endif /* HW_VFIO_VFIO_COMMON_H */
> diff --git a/include/migration/cpr.h b/include/migration/cpr.h
> index 07858e9..d09b657 100644
> --- a/include/migration/cpr.h
> +++ b/include/migration/cpr.h
> @@ -32,7 +32,9 @@ void cpr_state_close(void);
>   struct QIOChannel *cpr_state_ioc(void);
>   
>   bool cpr_incoming_needed(void *opaque);
> +void cpr_kvm_close(void);
>   
> +void cpr_transfer_init(void);
>   QEMUFile *cpr_transfer_output(MigrationChannel *channel, Error **errp);
>   QEMUFile *cpr_transfer_input(MigrationChannel *channel, Error **errp);
>   
> diff --git a/include/system/kvm.h b/include/system/kvm.h
> index 7cc60d2..4896a3c 100644
> --- a/include/system/kvm.h
> +++ b/include/system/kvm.h
> @@ -195,6 +195,7 @@ bool kvm_has_sync_mmu(void);
>   int kvm_has_vcpu_events(void);
>   int kvm_max_nested_state_length(void);
>   int kvm_has_gsi_routing(void);
> +void kvm_close(void);
>   
>   /**
>    * kvm_arm_supports_user_irq
> diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
> index a317783..3d3a557 100644
> --- a/accel/kvm/kvm-all.c
> +++ b/accel/kvm/kvm-all.c
> @@ -515,16 +515,23 @@ static int do_kvm_destroy_vcpu(CPUState *cpu)
>           goto err;
>       }
>   
> +    /* If I am the CPU that created coalesced_mmio_ring, then discard it */
> +    if (s->coalesced_mmio_ring == (void *)cpu->kvm_run + PAGE_SIZE) {
> +        s->coalesced_mmio_ring = NULL;
> +    }
> +
>       ret = munmap(cpu->kvm_run, mmap_size);
>       if (ret < 0) {
>           goto err;
>       }
> +    cpu->kvm_run = NULL;
>   
>       if (cpu->kvm_dirty_gfns) {
>           ret = munmap(cpu->kvm_dirty_gfns, s->kvm_dirty_ring_bytes);
>           if (ret < 0) {
>               goto err;
>           }
> +        cpu->kvm_dirty_gfns = NULL;
>       }
>   
>       kvm_park_vcpu(cpu);
> @@ -608,6 +615,31 @@ err:
>       return ret;
>   }
>   
> +void kvm_close(void)
> +{
> +    CPUState *cpu;
> +
> +    if (!kvm_state || kvm_state->fd == -1) {
> +        return;
> +    }
> +
> +    CPU_FOREACH(cpu) {
> +        cpu_remove_sync(cpu);
> +        close(cpu->kvm_fd);
> +        cpu->kvm_fd = -1;
> +        close(cpu->kvm_vcpu_stats_fd);
> +        cpu->kvm_vcpu_stats_fd = -1;
> +    }
> +
> +    if (kvm_state && kvm_state->fd != -1) {
> +        close(kvm_state->vmfd);
> +        kvm_state->vmfd = -1;
> +        close(kvm_state->fd);
> +        kvm_state->fd = -1;
> +    }
> +    kvm_state = NULL;
> +}
> +
>   /*
>    * dirty pages logging control
>    */
> diff --git a/accel/stubs/kvm-stub.c b/accel/stubs/kvm-stub.c
> index ecfd763..97dacb3 100644
> --- a/accel/stubs/kvm-stub.c
> +++ b/accel/stubs/kvm-stub.c
> @@ -134,3 +134,8 @@ int kvm_create_guest_memfd(uint64_t size, uint64_t flags, Error **errp)
>   {
>       return -ENOSYS;
>   }
> +
> +void kvm_close(void)
> +{
> +    return;
> +}
> diff --git a/hw/vfio/helpers.c b/hw/vfio/helpers.c
> index d0dbab1..af1db2f 100644
> --- a/hw/vfio/helpers.c
> +++ b/hw/vfio/helpers.c
> @@ -117,6 +117,16 @@ bool vfio_get_info_dma_avail(struct vfio_iommu_type1_info *info,
>   int vfio_kvm_device_fd = -1;
>   #endif
>   
> +void vfio_kvm_device_close(void)
> +{
> +#ifdef CONFIG_KVM
> +    if (vfio_kvm_device_fd != -1) {
> +        close(vfio_kvm_device_fd);
> +        vfio_kvm_device_fd = -1;
> +    }
> +#endif
> +}
> +
>   int vfio_kvm_device_add_fd(int fd, Error **errp)
>   {
>   #ifdef CONFIG_KVM
> diff --git a/hw/vfio/vfio-stubs.c b/hw/vfio/vfio-stubs.c
> new file mode 100644
> index 0000000..a4c8b56
> --- /dev/null
> +++ b/hw/vfio/vfio-stubs.c
> @@ -0,0 +1,13 @@
> +/*
> + * Copyright (c) 2025 Oracle and/or its affiliates.
> + *
> + * SPDX-License-Identifier: GPL-2.0-or-later
> + */
> +
> +#include "qemu/osdep.h"
> +#include "hw/vfio/vfio-device.h"
> +
> +void vfio_kvm_device_close(void)
> +{
> +    return;
> +}
> diff --git a/migration/cpr-transfer.c b/migration/cpr-transfer.c
> index e1f1403..396558f 100644
> --- a/migration/cpr-transfer.c
> +++ b/migration/cpr-transfer.c
> @@ -17,6 +17,24 @@
>   #include "migration/vmstate.h"
>   #include "trace.h"
>   
> +static int cpr_transfer_notifier(NotifierWithReturn *notifier,
> +                                 MigrationEvent *e,
> +                                 Error **errp)
> +{
> +    if (e->type == MIG_EVENT_PRECOPY_DONE) {
> +        cpr_kvm_close();
> +    }
> +    return 0;
> +}
> +
> +void cpr_transfer_init(void)
> +{
> +    static NotifierWithReturn notifier;
> +
> +    migration_add_notifier_mode(&notifier, cpr_transfer_notifier,
> +                                MIG_MODE_CPR_TRANSFER);
> +}
> +
>   QEMUFile *cpr_transfer_output(MigrationChannel *channel, Error **errp)
>   {
>       MigrationAddress *addr = channel->addr;
> diff --git a/migration/cpr.c b/migration/cpr.c
> index a50a57e..49fb0a5 100644
> --- a/migration/cpr.c
> +++ b/migration/cpr.c
> @@ -7,12 +7,14 @@
>   
>   #include "qemu/osdep.h"
>   #include "qapi/error.h"
> +#include "hw/vfio/vfio-device.h"
>   #include "migration/cpr.h"
>   #include "migration/misc.h"
>   #include "migration/options.h"
>   #include "migration/qemu-file.h"
>   #include "migration/savevm.h"
>   #include "migration/vmstate.h"
> +#include "system/kvm.h"
>   #include "system/runstate.h"
>   #include "trace.h"
>   
> @@ -264,3 +266,9 @@ bool cpr_incoming_needed(void *opaque)
>       MigMode mode = migrate_mode();
>       return mode == MIG_MODE_CPR_TRANSFER;
>   }
> +
> +void cpr_kvm_close(void)
> +{
> +    kvm_close();
> +    vfio_kvm_device_close();
> +}
> diff --git a/migration/migration.c b/migration/migration.c
> index 4098870..8f23cff 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -337,6 +337,7 @@ void migration_object_init(void)
>   
>       ram_mig_init();
>       dirty_bitmap_mig_init();
> +    cpr_transfer_init();
>   
>       /* Initialize cpu throttle timers */
>       cpu_throttle_init();
> diff --git a/hw/vfio/meson.build b/hw/vfio/meson.build
> index 73d29f9..98134a7 100644
> --- a/hw/vfio/meson.build
> +++ b/hw/vfio/meson.build
> @@ -17,6 +17,8 @@ vfio_ss.add(when: 'CONFIG_VFIO_IGD', if_true: files('igd.c'))
>   
>   specific_ss.add_all(when: 'CONFIG_VFIO', if_true: vfio_ss)
>   
> +system_ss.add(when: 'CONFIG_VFIO', if_false: files('vfio-stubs.c'))
> +
>   system_ss.add(when: 'CONFIG_VFIO_XGMAC', if_true: files('calxeda-xgmac.c'))
>   system_ss.add(when: 'CONFIG_VFIO_AMD_XGBE', if_true: files('amd-xgbe.c'))
>   system_ss.add(when: 'CONFIG_VFIO', if_true: files(