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

Niklas Schnelle
2021-12-16T14:39:46Z

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@linux.ibm.com>
> > > ---
> > > 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
you prefer to use __rpcit() directly I would rename it to zpci_rpcit().

>

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