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

[Raphael Norwitz]

On Wed, Jan 05, 2022 at 11:18:52AM +0000, Stefan Hajnoczi wrote:
> On Wed, Dec 15, 2021 at 10:29:55PM +0000, Raphael Norwitz wrote:
> > diff --git a/subprojects/libvhost-user/libvhost-user.c 
> > b/subprojects/libvhost-user/libvhost-user.c
> > index 74a9980194..2f465a4f0e 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)) {
> > @@ -831,25 +832,25 @@ vu_rem_mem_reg(VuDev *dev, VhostUserMsg *vmsg) {
> >              VuDevRegion *r = &dev->regions[i];
> >              void *m = (void *) (uintptr_t) r->mmap_addr;
> >  
> > -            if (m) {
> > +            if (m && !found) {
> >                  munmap(m, r->size + r->mmap_offset);
> >              }
> 
> Why is only the first region unmapped? My interpretation of
> vu_add_mem_reg() is that it mmaps duplicate regions to unique mmap_addr
> addresses, so we need to munmap each of them.

I agree - I will remove the found check here.

>
> >  
> > -            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--;
> > +
> > +            found = true;
> >          }
> 
> i-- is missing. dev->regions[] has been shortened so we need to check
> the same element again.

Ack