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Re: [RFC PATCH v2 1/3] vfio: Move the saving of the config space to the

From: Kirti Wankhede
Subject: Re: [RFC PATCH v2 1/3] vfio: Move the saving of the config space to the right place in VFIO migration
Date: Thu, 18 Feb 2021 20:15:06 +0530
User-agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0

On 1/27/2021 3:06 AM, Alex Williamson wrote:
On Thu, 10 Dec 2020 10:21:21 +0800
Shenming Lu <lushenming@huawei.com> wrote:

On 2020/12/10 2:34, Alex Williamson wrote:
On Wed, 9 Dec 2020 13:29:47 +0100
Cornelia Huck <cohuck@redhat.com> wrote:
On Wed, 9 Dec 2020 16:09:17 +0800
Shenming Lu <lushenming@huawei.com> wrote:
On ARM64 the VFIO SET_IRQS ioctl is dependent on the VM interrupt
setup, if the restoring of the VFIO PCI device config space is
before the VGIC, an error might occur in the kernel.

So we move the saving of the config space to the non-iterable
process, so that it will be called after the VGIC according to
their priorities.

As for the possible dependence of the device specific migration
data on it's config space, we can let the vendor driver to
include any config info it needs in its own data stream.
(Should we note this in the header file linux-headers/linux/vfio.h?)

Given that the header is our primary source about how this interface
should act, we need to properly document expectations about what will
be saved/restored when there (well, in the source file in the kernel.)
That goes in both directions: what a userspace must implement, and what
a vendor driver can rely on.

Yeah, in order to make the vendor driver and QEMU cooperate better, we might
need to document some expectations about the data section in the migration

[Related, but not a todo for you: I think we're still missing proper
documentation of the whole migration feature.]

Yes, we never saw anything past v1 of the documentation patch.  Thanks,

I'll get back on this and send next version soon.

By the way, is there anything unproper with this patch? Wish your suggestion. 

I'm really hoping for some feedback from Kirti, I understand the NVIDIA
vGPU driver to have some dependency on this.  Thanks,

NVIDIA driver doesn't use device config space value/information during device data restoration, so we are good with this change.



Signed-off-by: Shenming Lu <lushenming@huawei.com>
  hw/vfio/migration.c | 25 +++++++++++++++----------
  1 file changed, 15 insertions(+), 10 deletions(-)


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