netdev - Re: [PATCH] vhost_vdpa: fix unmap process in no-batch mode

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Date:   Tue, 11 Apr 2023 17:13:41 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Cindy Lu <lulu@...hat.com>
Cc:     mst@...hat.com, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org
Subject: Re: [PATCH] vhost_vdpa: fix unmap process in no-batch mode

On Tue, Apr 11, 2023 at 3:29 PM Cindy Lu <lulu@...hat.com> wrote:
>
> On Tue, Apr 11, 2023 at 11:10 AM Jason Wang <jasowang@...hat.com> wrote:
> >
> > On Mon, Apr 10, 2023 at 11:01 PM Cindy Lu <lulu@...hat.com> wrote:
> > >
> > > While using the no-batch mode, the process will not begin with
> > > VHOST_IOTLB_BATCH_BEGIN, so we need to add the
> > > VHOST_IOTLB_INVALIDATE to get vhost_vdpa_as, the process is the
> > > same as VHOST_IOTLB_UPDATE
> > >
> > > Signed-off-by: Cindy Lu <lulu@...hat.com>
> > > ---
> > >  drivers/vhost/vdpa.c | 1 +
> > >  1 file changed, 1 insertion(+)
> > >
> > > diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> > > index 7be9d9d8f01c..32636a02a0ab 100644
> > > --- a/drivers/vhost/vdpa.c
> > > +++ b/drivers/vhost/vdpa.c
> > > @@ -1074,6 +1074,7 @@ static int vhost_vdpa_process_iotlb_msg(struct vhost_dev *dev, u32 asid,
> > >                 goto unlock;
> > >
> > >         if (msg->type == VHOST_IOTLB_UPDATE ||
> > > +           msg->type == VHOST_IOTLB_INVALIDATE ||
> >
> > I'm not sure I get here, invalidation doesn't need to create a new AS.
> >
> > Or maybe you can post the userspace code that can trigger this issue?
> >
> > Thanks
> >
> sorry I didn't write it clearly
> For this issue can reproduce in vIOMMU no-batch mode support because
> while the vIOMMU enabled, it will
> flash a large memory to unmap, and this memory are haven't been mapped
> before, so this unmapping will fail
>
> qemu-system-x86_64: failed to write, fd=12, errno=14 (Bad address)
> qemu-system-x86_64: vhost_vdpa_dma_unmap(0x7fa26d1dd190, 0x0,
> 0x80000000) = -5 (Bad address)

So if this is a simple unmap, which error condition had you met in
vhost_vdpa_process_iotlb_msg()?

I think you need to trace to see what happens. For example:

1) can the code pass asid_to_iotlb()
2) if not, ASID 0 has been deleted since all the mappings have been unmapped

if ASID 0 has been completely unmap, any reason we need to unmap it
again? And do we need to drop the vhost_vdpa_remove_as() from both

1) vhost_vdpa_unmap()
and
2) vhost_vdpa_process_iotlb_msg()
?

Thanks

> qemu-system-x86_64: failed to write, fd=12, errno=14 (Bad address)
> ....
> in batch mode this operation will begin with VHOST_IOTLB_BATCH_BEGIN,
> so don't have this issue
>
> Thanks
> cindy
> > >             msg->type == VHOST_IOTLB_BATCH_BEGIN) {
> > >                 as = vhost_vdpa_find_alloc_as(v, asid);
> > >                 if (!as) {
> > > --
> > > 2.34.3
> > >
> >
>