Re: [Qemu-devel] [RFC 35/38] cputlb: use cpu_tcg_sched_work for tlb_flush_all

[Peter Maydell]

On 1 September 2015 at 20:38, Emilio G. Cota <address@hidden> wrote:
> I can replicate it; what's happening is that tlb_flush_all calls
> cpu_loop_exit(), then re-enters the cpu loop, performs the
> job while other CPUs are asleep(i.e. __tlb_flush_all in this case),
> but then when it continues execution it loads the same instruction
> (say a TLBIALLIS) again. So we end up with the same CPU calling
> tlb_flush_all in an infinite loop.
>
> A possible way to fix this is to finish the TB right after the
> helper and then add a flag in cpu_sched_work to not call
> cpu_exit_loop, raising an exit interrupt instead.

Sounds like a good idea.

> (Note that cpu_exit_loop is still necessary when doing work
> out-of-band wrt to execution, e.g. we *want* to come back
> to the same PC when doing a tb_flush.)

Really? I haven't looked at any of this code, but that sounds
a bit odd...

> I've tried doing this but I can't see an obvious place to insert
> the call to tcg_gen_exit_tb()--I see the calls to the TLB helpers
> are embedded in structs that I presume are called by some generic
> helper code. A little bit of help here would be appreciated, I'm
> not very familiar with target-arm.

The code (for 32-bit) is in disas_coproc_insn(). Any coprocessor
which isn't a CP_SPECIAL case (ie NOP or WFI) will always be the last
thing in its TB anyway, unless this is suppressed with the
ARM_CP_SUPPRESS_TB_END flag in the reginfo struct.

thanks
-- PMM