Xen when using the SR - IOV nic xl pci - failed to detach-CodePudding

Hi,
I 've'll a need to PCI hotplug devices between dom0 and domU using SR - IOV NIC. But I' m experiencing the problems when trying to detach VF wining one PV guests.
I can attach VF to DomU successful as follow:

reference

# xl pci - assignable - list
0000:05:10. 0
0000:05:10.
2# xl pci - attach 1 05:10. 0
2 # xl pci - attach 2 05:10.

It seems that everything is working fine and It can work well in DomU. But when I detach VF It report errors as follow:

reference

# xl pci - detach 2 05:10. 2
Libxl: error: libxl_device. C: 1269: libxl__wait_for_backend: Backend/local/domain/0/Backend/pci/2/0 not ready

Each guest config is the same like this:
The

reference

name="ubuntu - pv - 1"
Bootloader="pygrub"
The memory=256
Vcpus=1
2 vif is based=[' bridge=xenbr0]
Disk=[' file:/home/ye/ubuntu - pv/ubuntu -/ubuntu - pv pv - 1-1. The img, xvda, rw ']
Pci_permissive=1

Follow xl dmesg log:
The

reference

Xen 4.9.1
(XEN) XEN version 4.9.1 ye (@) (GCC (GCC) 4.8.5 20150623 (Red Hat 4.8.5-28)) the debug=n Mon Jun 4 11:34:35 CST 2018
(XEN) Latest ChangeSet:
(XEN) Bootloader: GRUB 2.02 beta 2 ~
(XEN) Command line: placeholder dom0_mem=2048 m, 2048 m dom0_max_vcpus=Max: 4 iommu=dom0 - passthrough
(XEN) XEN image load base address: 0
(XEN) Video information:
(XEN) VGA is 80 x25 text mode, the font 8 x16
(XEN) VBE varies/DDC the methods: none; EDID transfer time: 0 seconds
(XEN) EDID info not retrieved because no DDC retrieval method detected
(XEN) Disc information:
1 the MBR (XEN) Found signatures
(XEN) Found 4 EDD information structures
(XEN) XEN - e820 RAM map:
C000 (XEN) 0000000000000000-000000000009 (usable)
(XEN) a0000 c000 000000000009-00000000000 (reserved)
E0000 (XEN) 00000000000-0000000000100000 (reserved)
A289000 (XEN) 0000000000100000-000000007 (usable)
(XEN) af0b000 a289000 000000007-000000007 (reserved)
(XEN) b93b000 af0b000 000000007-000000007 (ACPI NVS)
(XEN) bab7000 b93b000 000000007-000000007 (ACPI data)
(XEN) bae9000 bab7000 000000007-000000007 (usable)
(XEN) baff000 bae9000 000000007-000000007 (ACPI data)
(XEN) bb00000 baff000 000000007-000000007 (usable)
Bb00000 (XEN) 000000007-0000000090000000 (reserved)
(XEN) fedac000 feda8000 00000000-00000000 (reserved)
Ff310000 (XEN) 00000000-0000000100000000 (reserved)
(XEN) 0000000100000000-0000000880000000 (usable)
(XEN) New XEN image base address: 0 x79c00000
ACPI (XEN) : RSDP fe320 000, 0024 (r2 DELL)
ACPI (XEN) : 7 bab50e8 XSDT, 00 BC (r1 DELL PE_SC3 0 1000013)
ACPI (XEN) : 7 bab1000 FACP, 00 f4 (r4 DELL DELL PE_SC3 0 1)
ACPI (XEN) : 7 ba99000 DSDT, 10768 (r2 DELL PE_SC3 3 DELL 1)
ACPI (XEN) : 7 b8e3000 both FACS, 0040
ACPI (XEN) : 7 bab4000 MCEJ, 0130 1 INTL (r1 INTEL 100000 d)
ACPI (XEN) : 7 bab3000 WD__, 0134 (r1 DELL PE_SC3 DELL 1)
ACPI (XEN) : 7 bab2000 SLIC, 0024 (r1 DELL PE_SC3 DELL 1)
ACPI (XEN) : 7 bab0000 HPET, 0038 (r1 DELL PE_SC3 DELL 1)
ACPI (XEN) : 7 baaf000 APIC, 0 afc (r2 DELL DELL PE_SC3 0 1)
ACPI (XEN) : 7 baae000 MCFG, 003 c (r1 DELL PE_SC3 DELL 1)
ACPI (XEN) : MSCT baad000 7, 0090 (r1 DELL PE_SC3 DELL 1)
ACPI (XEN) : 7 baac000 SLIT, 006 c (r1 DELL PE_SC3 DELL 1)
ACPI (XEN) : 7 baaa000 SRAT, 1130 (r3 DELL PE_SC3 DELL 1)
ACPI (XEN) : 7 b956000 SSDT, 1424 a9 (r2 DELL PE_SC3 4000 INTL 20121114)
ACPI (XEN) : 7 b953000 SSDT, 217 f (r2 DELL PE_SC3 INTL 20121114)
ACPI (XEN) : 7 b952000 SSDT, 006 e (r2 DELL PE_SC3 INTL 20121114)
ACPI (XEN) : 7 b951000 PRAD, 0132 (r2 DELL PE_SC3 INTL 20121114)
ACPI (XEN) : 7 bafe000 DMAR, 0120 (r1 DELL PE_SC3 DELL 1)
ACPI (XEN) : 7 bafd000 HEST, 017 c (r1 DELL PE_SC3 2 DELL 1)
7 bafc000 (XEN) ACPI: BERT, 0030 (r1 DELL PE_SC3 2 DELL 1)
ACPI (XEN) : ERST bafb000 7, 0230 (r1 DELL PE_SC3 2 DELL 1)
ACPI (XEN) : 7 bafa000 EINJ, 0150 (r1 DELL PE_SC3 2 DELL 1)
(XEN) System RAM: 32674 MB (33458528 KB)
(XEN) SRAT: Node 1 has no memory. The BIOS Bug or mis - configured hardware?
(XEN) Domain heap initialised DMA width 32 bits
ACPI (XEN) : 32/64 x both FACS address mismatch in FADT - 7 b8e3000/0000000000000000, using 32
(XEN) IOAPIC [0] : apic_id 8, 32 version, address 0 xfec00000, GSI 0-23
(XEN) IOAPIC [1] : apic_id 9, 32 version, address 0 xfec01000, GSI 24-47
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