Re: [PATCH 23/32] KVM: s390: pci: handle refresh of PCI translations

[Matthew Rosato]

On 12/16/21 9:39 AM, Niklas Schnelle wrote:
> On Tue, 2021-12-14 at 12:54 -0500, Matthew Rosato wrote:
> > On 12/14/21 11:59 AM, Pierre Morel wrote:
> > > On 12/7/21 21:57, Matthew Rosato wrote:
> > > > Add a routine that will perform a shadow operation between a guest
> > > > and host IOAT.  A subsequent patch will invoke this in response to
> > > > an 04 RPCIT instruction intercept.
> > > >
> > > > Signed-off-by: Matthew Rosato <mjrosato@xxxxxxxxxxxxx>
> > > > ---
> > > >    arch/s390/include/asm/kvm_pci.h |   1 +
> > > >    arch/s390/include/asm/pci_dma.h |   1 +
> > > >    arch/s390/kvm/pci.c             | 191 ++++++++++++++++++++++++++++++++
> > > >    arch/s390/kvm/pci.h             |   4 +-
> > > >    4 files changed, 196 insertions(+), 1 deletion(-)
> ---8<---
> > > > +
> > > > +int kvm_s390_pci_refresh_trans(struct kvm_vcpu *vcpu, unsigned long req,
> > > > +                   unsigned long start, unsigned long size)
> > > > +{
> > > > +    struct zpci_dev *zdev;
> > > > +    u32 fh;
> > > > +    int rc;
> > > > +
> > > > +    /* If the device has a SHM bit on, let userspace take care of
> > > > this */
> > > > +    fh = req >> 32;
> > > > +    if ((fh & aift.mdd) != 0)
> > > > +        return -EOPNOTSUPP;
> > >
> > > I think you should make this check in the caller.
> >
> > OK
> >
> > > > +
> > > > +    /* Make sure this is a valid device associated with this guest */
> > > > +    zdev = get_zdev_by_fh(fh);
> > > > +    if (!zdev || !zdev->kzdev || zdev->kzdev->kvm != vcpu->kvm)
> > > > +        return -EINVAL;
> > > > +
> > > > +    /* Only proceed if the device is using the assist */
> > > > +    if (zdev->kzdev->ioat.head[0] == 0)
> > > > +        return -EOPNOTSUPP;
> > >
> > > Using the assist means using interpretation over using interception and
> > > legacy vfio-pci. right?
> >
> > Right - more specifically that the IOAT assist feature was never set via
> > the vfio feature ioctl, so we can't handle the RPCIT for this device and
> > so throw to userspace.
> >
> > The way the QEMU series is being implemented, a device using
> > interpretation will always have the IOAT feature set on.
> >
> > > > +
> > > > +    rc = dma_table_shadow(vcpu, zdev, start, size);
> > > > +    if (rc > 0)
> > > > +        rc = zpci_refresh_trans((u64) zdev->fh << 32, start, size);
> > >
> > > Here you lose the status reported by the hardware.
> > > You should directly use __rpcit(fn, addr, range, &status);
> >
> > OK, I can have a look at doing this.
> >
> > @Niklas thoughts on how you would want this exported.  Renamed to
> > zpci_rpcit or so?
>
> Hmm with using __rpcit() directly we would lose the error reporting in
> s390dbf and this ist still kind of a RPCIT in the host. How about we
> add the status as an out parameter to zpci_refresh_trans()? But yes if

Another advantage of doing this would be that we then also keep the cc2 
retry logic in zpci_refresh_trans(), which would be nice.

However we do still lose the returned CC value from the instruction. 
But I think we can infer a CC1 from a nonzero status and a CC3 from a 
zero status so maybe this is OK too.

I think I will add the status parm to zpci_refresh_trans().

FWIW, I do also think it is likely we will end up with a s390dbf for 
kvm-pci at some point after this initial series.


> you prefer to use __rpcit() directly I would rename it to zpci_rpcit().

> >
>
> ---8<---