Re: [PATCH 1/3] accel/tcg: Set can_do_io at at start of lookup_tb_ptr helper

[Peter Maydell]

On Thu, 15 Feb 2024 at 15:02, Jonathan Cameron via
<qemu-devel@nongnu.org> wrote:
>
> From: Peter Maydell <peter.maydell@linaro.org>
>
> Peter posted this in the thread trying to fix x86 TCG handling
> of page tables in MMIO space (specifically emulated CXL interleaved memory)
> https://lore.kernel.org/qemu-devel/CAFEAcA_a_AyQ=Epz3_+CheAT8Crsk9mOu894wbNW_FywamkZiw@mail.gmail.com/#t
>
> Peter, are you happy to give your SoB on this one?
>
> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> ---
>  accel/tcg/cpu-exec.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
>
> diff --git a/accel/tcg/cpu-exec.c b/accel/tcg/cpu-exec.c
> index 977576ca14..52239a441f 100644
> --- a/accel/tcg/cpu-exec.c
> +++ b/accel/tcg/cpu-exec.c
> @@ -396,6 +396,14 @@ const void *HELPER(lookup_tb_ptr)(CPUArchState *env)
>      uint64_t cs_base;
>      uint32_t flags, cflags;
>
> +    /*
> +     * By definition we've just finished a TB, so I/O is OK.
> +     * Avoid the possibility of calling cpu_io_recompile() if
> +     * a page table walk triggered by tb_lookup() calling
> +     * probe_access_internal() happens to touch an MMIO device.
> +     * The next TB, if we chain to it, will clear the flag again.
> +     */
> +    cpu->neg.can_do_io = true;
>      cpu_get_tb_cpu_state(env, &pc, &cs_base, &flags);
>
>      cflags = curr_cflags(cpu);
> --

Happy to provide a
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

but I'd appreciate RTH's review to confirm this is the right
way to deal with the problem.

thanks
-- PMM