Number of the max supported VFs are different

Hi there, I have an Intel X520 network card, and I find the max supported VFs are different. Please check below outputs: # lspci -vvv -s 04:00.0 04:00.0 Ethernet controller: Intel Corporation Ethernet 10G 2P X520 Adapter (rev 01) ... Capabilities: [160 v1] Single Root I/O Virtualization (SR-IOV) IOVCap: Migration-, Interrupt Message Number: 000 IOVCtl: Enable- Migration- Interrupt- MSE- ARIHierarchy+ IOVSta: Migration- ** Initial VFs: 64, Total VFs: 64**, Number of VFs: 0, Function Dependency Link: 00 VF offset: 128, stride: 2, Device ID: 10ed Supported Page Size: 00000553, System Page Size: 00000001 Region 0: Memory at 0000000094400000 (64-bit, prefetchable) Region 3: Memory at 0000000094500000 (64-bit, prefetchable) VF Migration: offset: 00000000, BIR: 0 Kernel driver in use: ixgbe Kernel modules: ixgbe # cat /sys/class/net/enp4s0f0/device/sriov_totalvfs 63 # echo 64 > /sys/class/net/enp4s0f0/device/sriov_numvfs -bash: echo: write error: Numerical result out of range # echo 63 > /sys/class/net/enp4s0f0/device/sriov_numvfs # cat /sys/class/net/enp4s0f0/device/sriov_numvfs 63 The lspci command says the Total VFs supported is 64, while in the file "sriov_totalvfs" says it's 63. And the sriov_numvfs file will take precedence. Why are the numbers different? Just a little curious. Thank you! ------- Best Regards, Yalan Zhang IRC: yalzhang