Re: [PATCH 0/3] vhost-user: Fixes for VHOST_USER_ADD/REM_MEM_REG

[Stefan Hajnoczi]

On Thu, Apr 07, 2022 at 03:36:54PM +0200, Kevin Wolf wrote:
> While implementing a vhost-user-blk driver for libblkio, I found some
> problems with VHOST_USER_ADD/REM_MEM_REG both in the spec and in the
> implementations in QEMU and libvhost-user that this series addresses.
> 
> I also noticed that you can use REM_MEM_REG or SET_MEM_TABLE to unmap a
> memory region that is still in use (e.g. a block I/O request using
> addresses from the region has been started, but not completed yet),
> which is not great. I'm not sure how to fix this best, though.
> 
> We would have to wait for these requests to complete (maybe introduce a
> refcount and wait for it to drop to zero), but waiting seems impossible
> in libvhost-user because it doesn't have any main loop integration. Just
> failing the memory region removal would be safe, but potentially a
> rather awkward interface because clients would have to implement some
> retry logic.
> 
> Kevin Wolf (3):
>   docs/vhost-user: Clarifications for VHOST_USER_ADD/REM_MEM_REG
>   libvhost-user: Fix extra vu_add/rem_mem_reg reply
>   vhost-user: Don't pass file descriptor for VHOST_USER_REM_MEM_REG
> 
>  docs/interop/vhost-user.rst               | 17 +++++++++++++++++
>  hw/virtio/vhost-user.c                    |  2 +-
>  subprojects/libvhost-user/libvhost-user.c | 17 +++++++----------
>  3 files changed, 25 insertions(+), 11 deletions(-)
> 
> -- 
> 2.35.1
> 

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

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