Re: [PATCH 30/32] vfio-pci/zdev: add DTSM to clp group capability

[Matthew Rosato]

On 12/14/21 4:58 AM, Pierre Morel wrote:
> On 12/7/21 21:57, Matthew Rosato wrote:
> > The DTSM, or designation type supported mask, indicates what IOAT formats
> > are available to the guest.  For an interpreted device, userspace will 
> > not
> > know what format(s) the IOAT assist supports, so pass it via the
> > capability chain.  Since the value belongs to the Query PCI Function 
> > Group
> > clp, let's extend the existing capability with a new version.
> >
> > Signed-off-by: Matthew Rosato <mjrosato@xxxxxxxxxxxxx>
> > ---
> >   drivers/vfio/pci/vfio_pci_zdev.c | 9 ++++++---
> >   include/uapi/linux/vfio_zdev.h   | 3 +++
> >   2 files changed, 9 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/vfio/pci/vfio_pci_zdev.c 
> > b/drivers/vfio/pci/vfio_pci_zdev.c
> > index 85be77492a6d..342b59ed36c9 100644
> > --- a/drivers/vfio/pci/vfio_pci_zdev.c
> > +++ b/drivers/vfio/pci/vfio_pci_zdev.c
> > @@ -45,19 +45,22 @@ static int zpci_group_cap(struct zpci_dev *zdev, 
> > struct vfio_info_cap *caps)
> >   {
> >       struct vfio_device_info_cap_zpci_group cap = {
> >           .header.id = VFIO_DEVICE_INFO_CAP_ZPCI_GROUP,
> > -        .header.version = 1,
> > +        .header.version = 2,
> >           .dasm = zdev->dma_mask,
> >           .msi_addr = zdev->msi_addr,
> >           .flags = VFIO_DEVICE_INFO_ZPCI_FLAG_REFRESH,
> >           .mui = zdev->fmb_update,
> >           .noi = zdev->max_msi,
> >           .maxstbl = ZPCI_MAX_WRITE_SIZE,
>
> This, maxstbl, is not part of the patch but shouldn't we consider it too?
> The maxstbl is fixed for intercepted VFIO because the kernel is handling 
> the STBL instruction in behalf of the guest.
> Here the guest will use STBL directly.
>
> I think we should report the right maxstbl value.

I think we are OK, I think you missed the line that does this already, 
it was added in patch 27 when we wire up interpretive execution.  So, 
here we are defaulting to reporting ZPCI_MAX_WRITE_SIZE, and then ...

> > -        .version = zdev->version
> > +        .version = zdev->version,
> > +        .dtsm = 0
> >       };
> >       /* Some values are different for interpreted devices */
> > -    if (zdev->kzdev && zdev->kzdev->interp)
> > +    if (zdev->kzdev && zdev->kzdev->interp) {
> >           cap.maxstbl = zdev->maxstbl;

... Here we overwrite this with the hardware value only for interpreted 
devices.  Just like we are also now additionally doing for DTSM with 
this patch.

> > +        cap.dtsm = kvm_s390_pci_get_dtsm(zdev);
> > +    }
> >       return vfio_info_add_capability(caps, &cap.header, sizeof(cap));
> >   }
> > diff --git a/include/uapi/linux/vfio_zdev.h 
> > b/include/uapi/linux/vfio_zdev.h
> > index 1a5229b7bb18..b4c2ba8e71f0 100644
> > --- a/include/uapi/linux/vfio_zdev.h
> > +++ b/include/uapi/linux/vfio_zdev.h
> > @@ -47,6 +47,9 @@ struct vfio_device_info_cap_zpci_group {
> >       __u16 noi;        /* Maximum number of MSIs */
> >       __u16 maxstbl;        /* Maximum Store Block Length */
> >       __u8 version;        /* Supported PCI Version */
> > +    /* End of version 1 */
> > +    __u8 dtsm;        /* Supported IOAT Designations */
> > +    /* End of version 2 */
> >   };
> >   /**