On 17.02.25 17:40, Albert Esteve wrote:
Hi all,
Hi,
looks like our debugging session was successfu :)
One question below.
v3->v4
- Change mmap strategy to use RAM blocks
and subregions.
- Add new bitfield to qmp feature map
- Followed most review comments from
last iteration.
- Merged documentation patch again with
this one. Makes more sense to
review them together after all.
- Add documentation for MEM_READ/WRITE
messages.
The goal of this patch is to support
dynamic fd-backed memory maps initiated
from vhost-user backends.
There are many devices that could already
benefit of this feature, e.g.,
virtiofs or virtio-gpu.
After receiving the SHMEM_MAP/UNMAP request,
the frontend creates the RAMBlock form the
fd and maps it by adding it as a subregion
of the shared memory region container.
The VIRTIO Shared Memory Region list is
declared in the `VirtIODevice` struct
to make it generic.
TODO: There was a conversation on the
previous version around adding tests
to the patch (which I have acknowledged).
However, given the numerous changes
that the patch already has, I have
decided to send it early and collect
some feedback while I work on the
tests for the next iteration.
Given that I have been able to
test the implementation with
my local setup, I am more or less
confident that, at least, the code
is in a relatively sane state
so that no reviewing time is
wasted on broken patches.
This patch also includes:
- SHMEM_CONFIG frontend request that is
specifically meant to allow generic
vhost-user-device frontend to be able to
query VIRTIO Shared Memory settings from the
backend (as this device is generic and agnostic
of the actual backend configuration).
- MEM_READ/WRITE backend requests are
added to deal with a potential issue when having
multiple backends sharing a file descriptor.
When a backend calls SHMEM_MAP it makes
accessing to the region fail for other
backend as it is missing from their translation
table. So these requests are a fallback
for vhost-user memory translation fails.
Can you elaborate what the issue here is?
Why would SHMEM_MAP make accessing the region fail for other backends --
what makes this missing from their translation?
--
Cheers,
David / dhildenb
