linux-kernel - Re: [RFC v1 3/8] vhost: Add 3 new uapi to support iommufd

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Message-ID: <CACLfguW3NZawOL0ET2K7bmtGZuzQwUfJ2HSgnirswzZK1ayPnA@mail.gmail.com>
Date:   Wed, 8 Nov 2023 14:38:37 +0800
From:   Cindy Lu <lulu@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     mst@...hat.com, yi.l.liu@...el.com, jgg@...dia.com,
        linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org
Subject: Re: [RFC v1 3/8] vhost: Add 3 new uapi to support iommufd

On Wed, Nov 8, 2023 at 11:03 AM Jason Wang <jasowang@...hat.com> wrote:
>
> On Tue, Nov 7, 2023 at 2:57 PM Cindy Lu <lulu@...hat.com> wrote:
> >
> > On Mon, Nov 6, 2023 at 3:30 PM Jason Wang <jasowang@...hat.com> wrote:
> > >
> > > On Sat, Nov 4, 2023 at 1:17 AM Cindy Lu <lulu@...hat.com> wrote:
> > > >
> > > > VHOST_VDPA_SET_IOMMU_FD: bind the device to iommufd device
> > > >
> > > > VDPA_DEVICE_ATTACH_IOMMUFD_AS: Attach a vdpa device to an iommufd
> > > > address space specified by IOAS id.
> > > >
> > > > VDPA_DEVICE_DETACH_IOMMUFD_AS: Detach a vdpa device
> > > > from the iommufd address space
> > > >
> > > > Signed-off-by: Cindy Lu <lulu@...hat.com>
> > > > ---
> > >
> > > [...]
> > >
> > > > diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h
> > > > index f5c48b61ab62..07e1b2c443ca 100644
> > > > --- a/include/uapi/linux/vhost.h
> > > > +++ b/include/uapi/linux/vhost.h
> > > > @@ -219,4 +219,70 @@
> > > >   */
> > > >  #define VHOST_VDPA_RESUME              _IO(VHOST_VIRTIO, 0x7E)
> > > >
> > > > +/* vhost_vdpa_set_iommufd
> > > > + * Input parameters:
> > > > + * @iommufd: file descriptor from /dev/iommu; pass -1 to unset
> > > > + * @iommufd_ioasid: IOAS identifier returned from ioctl(IOMMU_IOAS_ALLOC)
> > > > + * Output parameters:
> > > > + * @out_dev_id: device identifier
> > > > + */
> > > > +struct vhost_vdpa_set_iommufd {
> > > > +       __s32 iommufd;
> > > > +       __u32 iommufd_ioasid;
> > > > +       __u32 out_dev_id;
> > > > +};
> > > > +
> > > > +#define VHOST_VDPA_SET_IOMMU_FD \
> > > > +       _IOW(VHOST_VIRTIO, 0x7F, struct vhost_vdpa_set_iommufd)
> > > > +
> > > > +/*
> > > > + * VDPA_DEVICE_ATTACH_IOMMUFD_AS -
> > > > + * _IOW(VHOST_VIRTIO, 0x7f, struct vdpa_device_attach_iommufd_as)
> > > > + *
> > > > + * Attach a vdpa device to an iommufd address space specified by IOAS
> > > > + * id.
> > > > + *
> > > > + * Available only after a device has been bound to iommufd via
> > > > + * VHOST_VDPA_SET_IOMMU_FD
> > > > + *
> > > > + * Undo by VDPA_DEVICE_DETACH_IOMMUFD_AS or device fd close.
> > > > + *
> > > > + * @argsz:     user filled size of this data.
> > > > + * @flags:     must be 0.
> > > > + * @ioas_id:   Input the target id which can represent an ioas
> > > > + *             allocated via iommufd subsystem.
> > > > + *
> > > > + * Return: 0 on success, -errno on failure.
> > > > + */
> > > > +struct vdpa_device_attach_iommufd_as {
> > > > +       __u32 argsz;
> > > > +       __u32 flags;
> > > > +       __u32 ioas_id;
> > > > +};
> > >
> > > I think we need to map ioas to vDPA AS, so there should be an ASID
> > > from the view of vDPA?
> > >
> > > Thanks
> > >
> > The qemu will have a structure save and  maintain this information,So
> > I didn't add this
> >  in kernel，we can add this but maybe only for check?
>
> I meant for example, a simulator has two AS. How can we attach an ioas
> to a specific AS with the above uAPI?
>
> Thank>
this   __u32 ioas_id here is alloc from the iommufd system. maybe I
need to change to new name iommuds_asid to
make this more clear
the process in qemu is

1) qemu want to use AS 0 (for example)
2) checking the existing asid. the asid 0 not used before
3 )alloc new asid from iommufd system, get new ioas_id (maybe 3 for example)
qemu will save this relation 3<-->0 in the driver.
4) setting the ioctl VDPA_DEVICE_ATTACH_IOMMUFD_AS to attach new ASID
to the kernel
5） while map the memory， qemu will use ASID 3 to map /umap
and use ASID 0 for legacy mode map/umap

So kernel here will not maintain the ioas_id from iommufd，
and this also make the code strange since there will 2 different asid
for the same AS, maybe we can save these information in the kernel
Thanks
cindy
> > Thanks
> > Cindy
> > > > +
> > > > +#define VDPA_DEVICE_ATTACH_IOMMUFD_AS \
> > > > +       _IOW(VHOST_VIRTIO, 0x82, struct vdpa_device_attach_iommufd_as)
> > > > +
> > > > +/*
> > > > + * VDPA_DEVICE_DETACH_IOMMUFD_AS
> > > > + *
> > > > + * Detach a vdpa device from the iommufd address space it has been
> > > > + * attached to. After it, device should be in a blocking DMA state.
> > > > + *
> > > > + * Available only after a device has been bound to iommufd via
> > > > + * VHOST_VDPA_SET_IOMMU_FD
> > > > + *
> > > > + * @argsz:     user filled size of this data.
> > > > + * @flags:     must be 0.
> > > > + *
> > > > + * Return: 0 on success, -errno on failure.
> > > > + */
> > > > +struct vdpa_device_detach_iommufd_as {
> > > > +       __u32 argsz;
> > > > +       __u32 flags;
> > > > +};
> > > > +
> > > > +#define VDPA_DEVICE_DETACH_IOMMUFD_AS \
> > > > +       _IOW(VHOST_VIRTIO, 0x83, struct vdpa_device_detach_iommufd_as)
> > > > +
> > > >  #endif
> > > > --
> > > > 2.34.3
> > > >
> > >
> >
>