Re: [PATCH] vhost-vdpa: skip TPM CRB memory section

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

On Wed, Nov 23, 2022 at 12:25:58PM +0100, Philippe Mathieu-Daudé wrote:
> On 23/11/22 08:23, Michael S. Tsirkin wrote:
> > On Wed, Nov 23, 2022 at 11:20:41AM +0400, Marc-André Lureau wrote:
> > > Hi
> > > 
> > > On Wed, Nov 23, 2022 at 12:32 AM Michael S. Tsirkin <mst@redhat.com> wrote:
> > > 
> > >      On Tue, Nov 22, 2022 at 06:53:49PM +0400, marcandre.lureau@redhat.com
> > >      wrote:
> > >      > From: Marc-André Lureau <marcandre.lureau@redhat.com>
> > >      >
> > >      > 851d6d1a0f ("vfio/common: remove spurious tpm-crb-cmd misalignment
> > >      > warning") removed the warning on vfio_listener_region_add() path.
> > >      >
> > >      > An error is reported for vhost-vdpa case:
> > >      > qemu-kvm: vhost_vdpa_listener_region_add received unaligned region
> > >      >
> > >      > Skip the CRB device.
> > >      >
> > >      > Fixes:
> > >      > https://bugzilla.redhat.com/show_bug.cgi?id=2141965
> > >      >
> > >      > Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> > >      > ---
> > >      >  hw/virtio/vhost-vdpa.c | 6 ++++++
> > >      >  1 file changed, 6 insertions(+)
> > >      >
> > >      > diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c
> > >      > index 7468e44b87..9d7206e4b8 100644
> > >      > --- a/hw/virtio/vhost-vdpa.c
> > >      > +++ b/hw/virtio/vhost-vdpa.c
> > >      > @@ -19,6 +19,7 @@
> > >      >  #include "hw/virtio/virtio-net.h"
> > >      >  #include "hw/virtio/vhost-shadow-virtqueue.h"
> > >      >  #include "hw/virtio/vhost-vdpa.h"
> > >      > +#include "sysemu/tpm.h"
> > >      >  #include "exec/address-spaces.h"
> > >      >  #include "migration/blocker.h"
> > >      >  #include "qemu/cutils.h"
> > >      > @@ -46,6 +47,11 @@ static bool vhost_vdpa_listener_skipped_section
> > >      (MemoryRegionSection *section,
> > >      >  {
> > >      >      Int128 llend;
> > >      >
> > >      > +    if (TPM_IS_CRB(section->mr->owner)) {
> > >      > +        /* The CRB command buffer has its base address unaligned. */
> > >      > +        return true;
> > >      > +    }
> > >      > +
> > > 
> > >      Quite a hack. We can't really keep adding dependency on random devices
> > > 
> > > 
> > > Agree it's not great. but it's not strictly a dependency. At least you can
> > > still build with !CONFIG_TPM.
> > 
> > but what does it have to do with tpm?
> > 
> > 
> > > 
> > >      to vhost. And would you add hacks like this to listeners?
> > >      Pls figure out what's special about this buffer.
> > >      Also if this section is unaligned then doesn't it break up
> > >      other aligned sections?
> > > 
> > > 
> > > See the original discussion:
> > > https://patchew.org/QEMU/20220208133842.112017-1-eric.auger@redhat.com/
> > > 20220208133842.112017-2-eric.auger@redhat.com/
> > > 
> > > It is not clear whether aligning the tpm-crb-cmd region would work (overlapping
> > > tpm-crb-mmio).
> > > 
> > > Peter Maydell said: "There's nothing that guarantees alignment for memory
> > > regions at all, whether they're RAM, IO or anything else.".
> > > 
> > > Maybe vfio/vhost should simply skip those odd regions silently.
> > 
> > 
> > How do we detect them? Are these regions not DMA-able on real hardware?
> 
> Are you suggesting expanding the Memory API?
> 
> - Add 'base_address_unaligned' to MemoryRegion structure (default to
>   false)
> 
> - Add memory_region_set_..._unaligned()
> 
> Then have TYPE_TPM_CRB use this API?

It's more of a "no_dma" isn't it? And I think we used to have
something like this, and later this morphed to device ram?

-- 
MST