linux-kernel - Re: [PATCH vfio] vfio/pci: remove msi domain on msi disable

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Message-ID: <91e0842c-1ba1-449d-b2d8-a3e2fc5ac95a@amd.com>
Date:   Mon, 18 Sep 2023 17:13:50 -0700
From:   "Nelson, Shannon" <shannon.nelson@....com>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     alex.williamson@...hat.com, kevin.tian@...el.com,
        reinette.chatre@...el.com, tglx@...utronix.de, kvm@...r.kernel.org,
        brett.creeley@....com, linux-kernel@...r.kernel.org,
        Leon Romanovsky <leonro@...dia.com>
Subject: Re: [PATCH vfio] vfio/pci: remove msi domain on msi disable

On 9/18/2023 4:32 PM, Jason Gunthorpe wrote:
> 
> On Mon, Sep 18, 2023 at 10:48:54AM -0700, Nelson, Shannon wrote:
> 
>> In our case, the VF device's msix count value found in PCI config space is
>> changed by device configuration management outside of the baremetal host and
>> read by the QEMU instance when it starts up, and then read by the vfio PCI
>> core when QEMU requests the first IRQ.
> 
> Oh, you definitely can't do that!
> 
> PCI config space is not allowed to change outside the OS's view and we
> added sriov_set_msix_vec_count() specifically as a way to provide the
> necessary synchronization between all the parts.
> 
> Randomly changing, what should be immutable, parts of the config space
> from under a running OS is just non-compliant PCI behavior.

Hmmm... I guess I need to have a little chat with my friendly HW/FW folks.

Thanks,
sln