Re: [PATCH v2 5/5] libvhost-user: handle removal of identical regions

[Raphael Norwitz <raphael.norwitz@nutanix.com>]

On Mon, Jan 10, 2022 at 09:58:01AM +0100, David Hildenbrand wrote:
> On 06.01.22 07:47, Raphael Norwitz wrote:
> > Today if QEMU (or any other VMM) has sent multiple copies of the same
> > region to a libvhost-user based backend and then attempts to remove the
> > region, only one instance of the region will be removed, leaving stale
> > copies of the region in dev->regions[].
> > 
> > This change resolves this by having vu_rem_mem_reg() iterate through all
> > regions in dev->regions[] and delete all matching regions.
> > 
> > Suggested-by: Stefan Hajnoczi <stefanha@redhat.com>
> > Signed-off-by: Raphael Norwitz <raphael.norwitz@nutanix.com>
> > ---
> >  subprojects/libvhost-user/libvhost-user.c | 26 ++++++++++++-----------
> >  1 file changed, 14 insertions(+), 12 deletions(-)
> > 
> > diff --git a/subprojects/libvhost-user/libvhost-user.c b/subprojects/libvhost-user/libvhost-user.c
> > index 0fe3aa155b..14482484d3 100644
> > --- a/subprojects/libvhost-user/libvhost-user.c
> > +++ b/subprojects/libvhost-user/libvhost-user.c
> > @@ -809,6 +809,7 @@ static bool
> >  vu_rem_mem_reg(VuDev *dev, VhostUserMsg *vmsg) {
> >      VhostUserMemoryRegion m = vmsg->payload.memreg.region, *msg_region = &m;
> >      int i;
> > +    bool found = false;
> >  
> >      if (vmsg->fd_num != 1 ||
> >          vmsg->size != sizeof(vmsg->payload.memreg)) {
> > @@ -835,21 +836,22 @@ vu_rem_mem_reg(VuDev *dev, VhostUserMsg *vmsg) {
> >                  munmap(m, r->size + r->mmap_offset);
> >              }
> >  
> > -            break;
> > +            /*
> > +             * Shift all affected entries by 1 to close the hole at index i and
> > +             * zero out the last entry.
> > +             */
> > +            memmove(dev->regions + i, dev->regions + i + 1,
> > +                    sizeof(VuDevRegion) * (dev->nregions - i - 1));
> > +            memset(dev->regions + dev->nregions - 1, 0, sizeof(VuDevRegion));
> > +            DPRINT("Successfully removed a region\n");
> > +            dev->nregions--;
> > +            i--;
> > +
> > +            found = true;
> 
> Maybe add a comment like
> 
> /* Continue the search for eventual duplicates. */

Ack - I'll add it.

> 
> 
> -- 
> Thanks,
> 
> David / dhildenb
>