Re: [Qemu-devel] [Qemu-arm] [PATCH 1/8] tcg: Clean up direct block chaining data fields

[Sergey Fedorov <serge.fdrv@gmail.com>]

On 29/03/16 19:26, Peter Maydell wrote:
> On 29 March 2016 at 09:31, Sergey Fedorov <serge.fdrv@gmail.com> wrote:
>> On 29/03/16 01:12, Richard Henderson wrote:
>>> On 03/24/2016 08:11 AM, Paolo Bonzini wrote:
>>>> There is also a case where a TB jumps to itself; it then appears twice
>>>> in the list with different values in the low bits, such as this:
>>>>
>>>>      tb->jmp_list_first = tb | 0;
>>>>       .--------------------'   |
>>>>       |                .-------'
>>>>      tb->jmp_list_next[0] = tb | 2;
>>> Of course, it begs the question of why TB would be in its own list,
>>> even if it does jump to itself.  We only need the points-to list in
>>> order to invalidate a TB and unlink it.  But if TB is being
>>> invalidated, we don't need to reset the jump within TB itself.
>> If we're going to move tb_phys_invalidate() outside of tb_lock, we
>> probably need to reset all jumps to the TB, even if it jumps to itself,
>> so that it eventually finish its execution.
> This is likely also the historical reason for the current code --
> originally we handled requesting a CPU exit by unlinking the TB,
> so you needed to be able to detach jumps-to-self (these days we do
> it by checking a flag at the start of each TB).

I'm not sure if CPU exit request is raised each time TB gets invalidated...

Kind regards,
Sergey