On 10/24/24 18:14, Pierrick Bouvier wrote:
On 10/24/24 09:25, Richard Henderson wrote:
On 10/23/24 23:20, Pierrick Bouvier wrote:
When instrumenting memory accesses for plugin, we force memory accesses
to use the slow path for mmu. [1]
This create a situation where we end up calling ptw_setl_slow.
Since this function gets called during a cpu_exec, start_exclusive then
hangs. This exclusive section was introduced initially for security
reasons [2].
I suspect this code path was never triggered, because ptw_setl_slow
would always be called transitively from cpu_exec, resulting in a hang.
[1]
https://gitlab.com/qemu-project/qemu/-/commit/6d03226b42247b68ab2f0b3663e0f624335a4055
[2] https://gitlab.com/qemu-project/qemu/-/issues/279
Fixes: https://gitlab.com/qemu-project/qemu/-/issues/2566
Signed-off-by: Pierrick Bouvier <pierrick.bouv...@linaro.org>
Oh, wow. I believe this will be fixed by
https://lore.kernel.org/qemu-devel/20241023033432.1353830-19-richard.hender...@linaro.org/
which is in a pending PR.
It might the issue by not triggering the situation we observed.
However, we still have a hidden dead code path where start_exclusive is called from
cpu_exec, not being related to the plugins.
You're right, this would affect mmio, were the os so careless as to place page
tables in mmio.
+ /* We are in cpu_exec, and start_exclusive can't be called directly.*/
+ g_assert(current_cpu && current_cpu->running);
+ cpu_exec_end(current_cpu);
Better to use env_cpu(in->env).
r~
