Re: [PATCH v2 0/3] virtio-gpu: fix blob unmapping sequence

["Alex Bennée" <alex.bennee@linaro.org>]

Manos Pitsidianakis <manos.pitsidianakis@linaro.org> writes:

> A hang was observed when running a small kernel that exercised VIRTIO 
> GPU under TCG. This is an edge-case and won't happen under typical 
> conditions.

Should I (or MST?) pull these into a tree for 10.0 or should they be
grabbed for when the tree opens with a Cc qemu-stable?

>
> When unmapping a blob object, its MemoryRegion's freeing is deferred to 
> the RCU thread. The hang's cause was determined to be a busy main loop 
> not allowing for the RCU thread to run because the kernel did not setup 
> any timers or had any interrupts on the way. While fixing the RCU thread 
> to run even if the guest CPU spins is a solution, it's easier to fix the 
> reason why the MemoryRegion isn't freed from the main loop instead.
>
> While at it, also restructure the 3 stage cleanup to immediately respond 
> to the guest if the MR happened to have had no other reference.
>
> PS: The hang can be reproduced by running this unikernel with TCG 
>
> https://git.codelinaro.org/manos.pitsidianakis/virtio-tests/-/tree/8c0ebe9395827e24aa5711186d499bf5de87cf63/virtio-test-suite
>
> v1 to v2:
>   - Add patch by Alex to prevent double-free when FlatView is destroyed 
>     from RCU thread.
>
> Alex Bennée (1):
>   hw/display: re-arrange memory region tracking
>
> Manos Pitsidianakis (2):
>   virtio-gpu: fix hang under TCG when unmapping blob
>   virtio-gpu: refactor async blob unmapping
>
>  include/exec/memory.h         |  1 +
>  hw/display/virtio-gpu-virgl.c | 60 ++++++++++++++++++++---------------
>  2 files changed, 35 insertions(+), 26 deletions(-)
>
>
> base-commit: 56c6e249b6988c1b6edc2dd34ebb0f1e570a1365

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro