Re: [PATCH V3 24/42] migration: close kvm after cpr

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

On 5/16/2025 1:14 PM, Peter Xu wrote:
> On Fri, May 16, 2025 at 10:35:44AM +0200, Cédric Le Goater wrote:
>> On 5/12/25 17:32, 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.
>>>
> 
> [1]
> 
>>> Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
>>
>> This patch doesn't build.
>>
>> /usr/bin/ld: libcommon.a.p/migration_cpr.c.o: in function `cpr_kvm_close':
>> ./build/../migration/cpr.c:260: undefined reference to `kvm_close'
> 
> And it'll be also good if this patch can keep copying the kvm maintainer
> (Paolo)..  I have Paolo copied.  So this patch is more of a kvm change not
> migration, afaict.  Maybe we should split this into two patches.
> 
> Steve, you could attach a cc line in this patch to make sure it won't be
> forgotten when you repost (at [1] above, I think git-send-email would
> remember that then):
> 
> Cc: Paolo Bonzini <pbonzini@redhat.com>

Righto.  My intention was to cc him on this specific patch and not the whole
series, which I did in V2 but forgot in V3.  Thanks for the tip on embedding
cc in the patch.

> Some other questions below.
> 
>>> ---
>>>    accel/kvm/kvm-all.c           | 28 ++++++++++++++++++++++++++++
>>>    hw/vfio/helpers.c             | 10 ++++++++++
>>>    include/hw/vfio/vfio-device.h |  2 ++
>>>    include/migration/cpr.h       |  2 ++
>>>    include/qemu/vfio-helpers.h   |  1 -
>>>    include/system/kvm.h          |  1 +
>>>    migration/cpr-transfer.c      | 18 ++++++++++++++++++
>>>    migration/cpr.c               |  8 ++++++++
>>>    migration/migration.c         |  1 +
>>>    9 files changed, 70 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
>>> index 278a506..d619448 100644
>>> --- a/accel/kvm/kvm-all.c
>>> +++ b/accel/kvm/kvm-all.c
>>> @@ -512,16 +512,23 @@ static int do_kvm_destroy_vcpu(CPUState *cpu)
>>>            goto err;
>>>        }
>>> +    /* If I am the CPU that created coalesced_mmio_ring, then discard it */
> 
> Are these "reset to NULL" below required or cleanup?  It's not yet clear to
> me when coalesced_mmio_ring isn't owned by the current CPU state.  Maybe
> also better to split this chunk with some commit message?

The pointers are not valid after this point.  Setting to NULL is cleanup, but
a best practice IMO.  The vcpus are paused, so nothing should be touching
coalesced_mmio_ring, and it does not matter in which order we destroy vcpus.

- Steve

>>> +    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);
>>> @@ -600,6 +607,27 @@ err:
>>>        return ret;
>>>    }
>>> +void kvm_close(void)
>>> +{
>>> +    CPUState *cpu;
>>> +
>>> +    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/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/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 fc6aa33..5f1ff10 100644
>>> --- a/include/migration/cpr.h
>>> +++ b/include/migration/cpr.h
>>> @@ -31,7 +31,9 @@ void cpr_state_close(void);
>>>    struct QIOChannel *cpr_state_ioc(void);
>>>    bool cpr_needed_for_reuse(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/qemu/vfio-helpers.h b/include/qemu/vfio-helpers.h
>>> index bde9495..a029036 100644
>>> --- a/include/qemu/vfio-helpers.h
>>> +++ b/include/qemu/vfio-helpers.h
>>> @@ -28,5 +28,4 @@ void qemu_vfio_pci_unmap_bar(QEMUVFIOState *s, int index, void *bar,
>>>                                 uint64_t offset, uint64_t size);
>>>    int qemu_vfio_pci_init_irq(QEMUVFIOState *s, EventNotifier *e,
>>>                               int irq_type, Error **errp);
>>> -
>>>    #endif
>>> diff --git a/include/system/kvm.h b/include/system/kvm.h
>>> index b690dda..cfaa94c 100644
>>> --- a/include/system/kvm.h
>>> +++ b/include/system/kvm.h
>>> @@ -194,6 +194,7 @@ 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/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 0b01e25..6102d04 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"
>>> @@ -252,3 +254,9 @@ bool cpr_needed_for_reuse(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 4697732..89e2026 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();
>>
>