Re: [Qemu-devel] [RFC 14/29] vhost+postcopy: Register new regions with the ufd

[Dr. David Alan Gilbert]

* Maxime Coquelin (address@hidden) wrote:
> 
> 
> On 06/28/2017 09:00 PM, Dr. David Alan Gilbert (git) wrote:
> > From: "Dr. David Alan Gilbert" <address@hidden>
> > 
> > When new regions are sent to the client using SET_MEM_TABLE, register
> > them with the userfaultfd.
> > 
> > Signed-off-by: Dr. David Alan Gilbert <address@hidden>
> > ---
> >   contrib/libvhost-user/libvhost-user.c | 33 
> > +++++++++++++++++++++++++++++++++
> >   1 file changed, 33 insertions(+)
> > 
> > diff --git a/contrib/libvhost-user/libvhost-user.c 
> > b/contrib/libvhost-user/libvhost-user.c
> > index 6de339fb7a..be7470e3a9 100644
> > --- a/contrib/libvhost-user/libvhost-user.c
> > +++ b/contrib/libvhost-user/libvhost-user.c
> > @@ -450,6 +450,39 @@ vu_set_mem_table_exec(VuDev *dev, VhostUserMsg *vmsg)
> >                      dev_region->mmap_addr);
> >           }
> > +        if (dev->postcopy_listening) {
> > +            /* We should already have an open ufd need to mark each memory
> > +             * range as ufd.
> > +             * Note: Do we need any madvises? Well it's not been accessed
> > +             * yet, still probably need no THP to be safe, discard to be 
> > safe?
> > +             */
> > +            struct uffdio_register reg_struct;
> > +            /* Note: We might need to go back to using mmap_addr and
> > +             * len + mmap_offset for * huge pages, but then we do hope not 
> > to
> > +             * see accesses in that area below the offset
> > +             */
> > +            reg_struct.range.start = (uintptr_t)(dev_region->mmap_addr +
> > +                                                 dev_region->mmap_offset);
> > +            reg_struct.range.len = dev_region->size;
> > +            reg_struct.mode = UFFDIO_REGISTER_MODE_MISSING;
> > +
> > +            if (ioctl(dev->postcopy_ufd, UFFDIO_REGISTER, &reg_struct)) {
> > +                vu_panic(dev, "%s: Failed to userfault region %d: 
> > (ufd=%d)%s\n",
> > +                         __func__, i, strerror(errno), dev->postcopy_ufd);
> Aren't the two last args swapped?

Fixed.
Thanks for spotting that; adding a GCC_FMT_ATTR(2, 3) before vu_panic
doesn't show any more from me, but there are a couple of existing cases
that look wrong;  I think they just need a * before them, but am not
100% sure.

Dave

> > +                continue;
> > +            }
> > +            if (!(reg_struct.ioctls & ((__u64)1 << _UFFDIO_COPY))) {
> > +                vu_panic(dev, "%s Region (%d) doesn't support COPY",
> > +                         __func__, i);
> > +                continue;
> > +            }
> > +            DPRINT("%s: region %d: Registered userfault for %llx + %llx\n",
> > +                    __func__, i, reg_struct.range.start, 
> > reg_struct.range.len);
> > +            /* TODO: Stash 'zero' support flags somewhere */
> > +            /* TODO: Get address back to QEMU */
> > +
> > +        }
> > +
> >           close(vmsg->fds[i]);
> >       }
> > 
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK