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Re: [Qemu-devel] [RFC 3/3] vhost-user: support programming VFIO group in
From: |
Alex Williamson |
Subject: |
Re: [Qemu-devel] [RFC 3/3] vhost-user: support programming VFIO group in master |
Date: |
Wed, 12 Sep 2018 10:34:43 -0600 |
On Wed, 12 Sep 2018 12:14:44 -0400
"Michael S. Tsirkin" <address@hidden> wrote:
> On Wed, Sep 12, 2018 at 04:04:00PM +0800, Tiwei Bie wrote:
> > On Mon, Jul 30, 2018 at 12:30:58PM +0300, Michael S. Tsirkin wrote:
> > [...]
> > >
> > > I generally wonder how are restarts of the backend handled
> > > with this approach: closing the VFIO device tends to reset
> > > the whole device.
> >
> > Hi Michael,
> >
> > I missed this comment previously.. This is a good point!
> > In this RFC, before sending the VFIO group fd to QEMU,
> > backend needs to close the VFIO device and unset the VFIO
> > container first. Otherwise, QEMU won't be able to set the
> > VFIO container for the VFIO group.
> >
> > Another option is to share the container fd instead of
> > the group fd to QEMU. In this case, backend won't need
> > to close any fd. But there is one problem that, it's
> > hard to unmap the old mappings, especially when QEMU
> > crashes.
>
> What are these old mappings and who creates them?
> If you want to just reset everything the way it was
> on open, surely it would be easy to add such a reset ioctl.
>
> > Do you have any suggestions? Thanks!
> >
> > Best regards,
> > Tiwei Bie
>
> Donnu. Alex, any thoughts? Which approach would you prefer?
The existing UNMAP_DMA ioctl for the vfio type1 IOMMU only requires
that an unmap does not bisect previous mappings, ie. a previous mapping
cannot be partially unmapped. Therefore you can already dump the
entire IOVA space for a container with one UNMAP_DMA call, iova = 0,
size = (u64)-1. Thanks,
Alex
- Re: [Qemu-devel] [RFC 3/3] vhost-user: support programming VFIO group in master, Tiwei Bie, 2018/09/12
- Re: [Qemu-devel] [RFC 3/3] vhost-user: support programming VFIO group in master, Michael S. Tsirkin, 2018/09/12
- Re: [Qemu-devel] [RFC 3/3] vhost-user: support programming VFIO group in master,
Alex Williamson <=
- Re: [Qemu-devel] [RFC 3/3] vhost-user: support programming VFIO group in master, Michael S. Tsirkin, 2018/09/12
- Re: [Qemu-devel] [RFC 3/3] vhost-user: support programming VFIO group in master, Alex Williamson, 2018/09/12
- Re: [Qemu-devel] [RFC 3/3] vhost-user: support programming VFIO group in master, Michael S. Tsirkin, 2018/09/12
- Re: [Qemu-devel] [RFC 3/3] vhost-user: support programming VFIO group in master, Alex Williamson, 2018/09/12
- Re: [Qemu-devel] [RFC 3/3] vhost-user: support programming VFIO group in master, Tian, Kevin, 2018/09/13