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

[Maxime Coquelin <maxime.coquelin@redhat.com>]

On 06/28/2017 09:00 PM, Dr. David Alan Gilbert (git) wrote:
> From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> 
> When new regions are sent to the client using SET_MEM_TABLE, register
> them with the userfaultfd.
> 
> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> ---
>   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?

> +                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]);
>       }
>   
>