target/i386: fix hang when using slow path for ptw_setl

target/i386: fix hang when using slow path for ptw_setl

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. This was fixed recently in [2] but the issue
still could appear out of plugins use case.

Since this function gets called during a cpu_exec, start_exclusive then
hangs. This exclusive section was introduced initially for security
reasons [3].

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/-/commit/115ade42d50144c15b74368d32dc734ea277d853
[2] https://gitlab.com/qemu-project/qemu/-/commit/88442869cf709f885a9c09fad00b96f802d58ffe in 9.0.x series
[3] https://gitlab.com/qemu-project/qemu/-/issues/279

Fixes: https://gitlab.com/qemu-project/qemu/-/issues/2566
Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-ID: <20241025175857.2554252-2-pierrick.bouvier@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
(cherry picked from commit 7ba055b49b74c4d2f4a338c5198485bdff373fb1)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
(Mjt: mention [2] in 9.0.x series)