Re: [EXT] Re: [PATCH v3] virtio-pci: correctly set virtio pci queue mem multiplier

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Feb 28, 2024 at 06:13:03AM +0000, Srujana Challa wrote:
> > Subject: [EXT] Re: [PATCH v3] virtio-pci: correctly set virtio pci queue mem
> > multiplier
> > 
> > External Email
> > 
> > ----------------------------------------------------------------------
> > On Fri, Feb 23, 2024 at 10:56:17AM +0530, Srujana Challa wrote:
> > > Currently, virtio_pci_queue_mem_mult function always returns 4K when
> > > VIRTIO_PCI_FLAG_PAGE_PER_VQ is set. But this won't work for vhost vdpa
> > > when host has page size other than 4K.
> > > This patch introduces a new property(host-page-per-vq) for vdpa use
> > > case to fix the same.
> > >
> > > Signed-off-by: Srujana Challa <schalla@marvell.com>
> > 
> > Looks good. I'd like to fail realize if both
> >    (proxy->flags & VIRTIO_PCI_FLAG_PAGE_PER_VQ) and
> >    (proxy->flags & VIRTIO_PCI_FLAG_HOST_PAGE_PER_VQ) so users do not
> > start depending on this combination.
> Could you confirm if we can add assertion for this case in virtio_pci_mem_mult() function?

No, reporting an error would be better since it's user-triggerable -
it is not nice to report user errors through assertions,
assertions are for conditions that can not be reached.


> > 
> > 
> > 
> > > ---
> > > v2->v3:
> > > - Modified property name, page-per-vdpa-vq to host-page-per-vq.
> > >
> > > v1->v2:
> > > - Introduced a new property to get virtqueue mem multiplier for
> > >   vdpa use case.
> > >
> > >  hw/virtio/virtio-pci.c         | 10 ++++++++--
> > >  include/hw/virtio/virtio-pci.h |  5 +++++
> > >  2 files changed, 13 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c index
> > > 1a7039fb0c..f29e60830b 100644
> > > --- a/hw/virtio/virtio-pci.c
> > > +++ b/hw/virtio/virtio-pci.c
> > > @@ -320,8 +320,12 @@ static bool
> > > virtio_pci_ioeventfd_enabled(DeviceState *d)
> > >
> > >  static inline int virtio_pci_queue_mem_mult(struct VirtIOPCIProxy
> > > *proxy)  {
> > > -    return (proxy->flags & VIRTIO_PCI_FLAG_PAGE_PER_VQ) ?
> > > -        QEMU_VIRTIO_PCI_QUEUE_MEM_MULT : 4;
> > > +    if (proxy->flags & VIRTIO_PCI_FLAG_PAGE_PER_VQ)
> > > +        return QEMU_VIRTIO_PCI_QUEUE_MEM_MULT;
> > > +    else if (proxy->flags & VIRTIO_PCI_FLAG_HOST_PAGE_PER_VQ)
> > > +        return qemu_real_host_page_size();
> > > +    else
> > > +        return 4;
> > >  }
> > >
> > >  static int virtio_pci_ioeventfd_assign(DeviceState *d, EventNotifier
> > > *notifier, @@ -2301,6 +2305,8 @@ static Property virtio_pci_properties[] =
> > {
> > >                      VIRTIO_PCI_FLAG_INIT_FLR_BIT, true),
> > >      DEFINE_PROP_BIT("aer", VirtIOPCIProxy, flags,
> > >                      VIRTIO_PCI_FLAG_AER_BIT, false),
> > > +    DEFINE_PROP_BIT("host-page-per-vq", VirtIOPCIProxy, flags,
> > > +                    VIRTIO_PCI_FLAG_HOST_PAGE_PER_VQ_BIT, false),
> > >      DEFINE_PROP_END_OF_LIST(),
> > >  };
> > >
> > > diff --git a/include/hw/virtio/virtio-pci.h
> > > b/include/hw/virtio/virtio-pci.h index 59d88018c1..81b6de4291 100644
> > > --- a/include/hw/virtio/virtio-pci.h
> > > +++ b/include/hw/virtio/virtio-pci.h
> > > @@ -43,6 +43,7 @@ enum {
> > >      VIRTIO_PCI_FLAG_INIT_FLR_BIT,
> > >      VIRTIO_PCI_FLAG_AER_BIT,
> > >      VIRTIO_PCI_FLAG_ATS_PAGE_ALIGNED_BIT,
> > > +    VIRTIO_PCI_FLAG_HOST_PAGE_PER_VQ_BIT,
> > >  };
> > >
> > >  /* Need to activate work-arounds for buggy guests at vmstate load. */
> > > @@ -89,6 +90,10 @@ enum {  #define
> > VIRTIO_PCI_FLAG_ATS_PAGE_ALIGNED \
> > >    (1 << VIRTIO_PCI_FLAG_ATS_PAGE_ALIGNED_BIT)
> > >
> > > +/* page per vdpa vq flag to be used for vhost vdpa backends */
> > > +#define VIRTIO_PCI_FLAG_HOST_PAGE_PER_VQ \
> > > +    (1 << VIRTIO_PCI_FLAG_HOST_PAGE_PER_VQ_BIT)
> > > +
> > >  typedef struct {
> > >      MSIMessage msg;
> > >      int virq;
> > > --
> > > 2.25.1