Re: [Qemu-devel] [RFC v2 15/32] vhost+postcopy: Register new regions with the ufd

[Marc-André Lureau]

Use "libvhost-user: " commit title tag/prefix?

On Thu, Aug 24, 2017 at 12:27 PM, Dr. David Alan Gilbert (git)
<address@hidden> 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 | 32 ++++++++++++++++++++++++++++++++
>  1 file changed, 32 insertions(+)
>
> diff --git a/contrib/libvhost-user/libvhost-user.c 
> b/contrib/libvhost-user/libvhost-user.c
> index e8accf11db..e6ab059a03 100644
> --- a/contrib/libvhost-user/libvhost-user.c
> +++ b/contrib/libvhost-user/libvhost-user.c
> @@ -449,6 +449,38 @@ 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;
> +            reg_struct.range.start = (uintptr_t)dev_region->mmap_addr;
> +            reg_struct.range.len = dev_region->size + 
> dev_region->mmap_offset;
> +            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 "
> +                              "@%p + %zx: (ufd=%d)%s\n",
> +                         __func__, i,
> +                         dev_region->mmap_addr,
> +                         dev_region->size + dev_region->mmap_offset,
> +                         dev->postcopy_ufd, strerror(errno));
> +                continue;

panic is supposed to be unrecoverable errors, so I would suggest to return here

> +            }
> +            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]);
>      }

This patch would be nicer if it compiles on !Linux / without userfault.


-- 
Marc-André Lureau