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

[David Hildenbrand <david@redhat.com>]

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. */


-- 
Thanks,

David / dhildenb