Comment 0 for bug 1894893

There are failed logs after resume from hibernation in NV6 (GPU passthrough size) VM in Azure:
[ 1432.153730] hv_pci 47505500-0001-0000-3130-444531334632: hv_irq_unmask() failed: 0x5
[ 1432.167910] hv_pci 47505500-0001-0000-3130-444531334632: hv_irq_unmask() failed: 0x5

This happens to the latest stable release of the linux-azure 5.4.0-1023.23 kernel and the latest mainline linux kernel.

How reproducible:
100%

Steps to Reproduce:
1. Start a Standard_NV6 VM in Azure and enable hibernation properly (please refer to https://bugs.launchpad.net/ubuntu/+source/linux-azure/+bug/1880032/comments/14 )

E.g. here I create a Generation-1 Ubuntu 20.04 Standard NV6_Promo (6 vcpus, 56 GiB memory) VM in East US 2.

2. Make sure the in-kernel open-source nouveau driver is loaded, or blacklist the nouveau driver and install the official Nvidia GPU driver (please follow https://docs.microsoft.com/en-us/azure/virtual-machines/linux/n-series-driver-setup : "Install GRID drivers on NV or NVv3-series VMs" -- the most important step to run the "./NVIDIA-Linux-x86_64-grid.run".)

3. Run hibernation from serial console
# systemctl hibernate

4. After hibernation finishes, start VM and check dmesg
# dmesg|grep fail

Actual results:
[ 1432.153730] hv_pci 47505500-0001-0000-3130-444531334632: hv_irq_unmask() failed: 0x5
[ 1432.167910] hv_pci 47505500-0001-0000-3130-444531334632: hv_irq_unmask() failed: 0x5

And /proc/interrupts shows that the GPU interrupts are no longer happening.

Expected results:
No failed logs, and the GPU interrupt should still happen after hibernation.

BUG FIX:
I made a fix here: https://lkml.org/lkml/2020/9/4/1268.

Without the patch, we see the error "hv_pci 47505500-0001-0000-3130-444531334632: hv_irq_unmask() failed: 0x5" during hibernation when the VM has the Nvidia GPU driver loaded, and after hibernation the GPU driver can no longer receive any MSI/MSI-X interrupts when we check /proc/interrupts.

With the patch, we should no longer see the error, and the GPU driver should still receive interrupts after hibernation.