Re: [Qemu-devel] [RFC PATCH V7 14/19] cpu: introduce tlb_flush*_all.

[Peter Maydell <peter.maydell@linaro.org>]

On 10 August 2015 at 16:54, Paolo Bonzini <pbonzini@redhat.com> wrote:
> On 10/08/2015 17:27, fred.konrad@greensocs.com wrote:
>> From: KONRAD Frederic <fred.konrad@greensocs.com>
>>
>> Some architectures allow to flush the tlb of other VCPUs. This is not a problem
>> when we have only one thread for all VCPUs but it definitely needs to be an
>> asynchronous work when we are in true multithreaded work.
>>
>> TODO: Some test case, I fear some bad results in case a VCPUs execute a barrier
>>       or something like that.
>>
>> Signed-off-by: KONRAD Frederic <fred.konrad@greensocs.com>
>> ---
>>  cputlb.c                | 76 +++++++++++++++++++++++++++++++++++++++++++++++++
>>  include/exec/exec-all.h |  2 ++
>>  2 files changed, 78 insertions(+)
>
> I still believe this should be a target-specific change.  This would
> also make it easier to do the remote TLB flush synchronously, as is the
> case on ARM (if I understand correctly).

ARM TLB flushes have to complete by the next barrier instruction
(or equivalent thing); so they're asynchronous but with a guest-controlled
synchronization point.

Also, compare the series I posted recently for adding missing
TLB operations:
https://lists.gnu.org/archive/html/qemu-devel/2015-08/msg00945.html
which adds support for flush-specific-mmuidx operations, which would
increase the number of primitives you're trying to support here.
That might argue for making this target-specific.

thanks
-- PMM