Re: [PATCH v3 41/42] target/arm: Implement FEAT_HAFDBS

[Peter Maydell]

On Fri, 7 Oct 2022 at 17:45, Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> On 10/7/22 06:47, Peter Maydell wrote:
> > Are there definitely no code paths where we might try to do
> > a page table walk with the iothread already locked ?
>
> I'll double-check, but another possibility is to simply perform the atomic 
> operation on
> the low 32-bits, where both AF and DB are located.  Another trick I learned 
> from x86...

Doesn't that cause a problem where we don't detect that some other
CPU wrote to the high 32 bits of the descriptor ? We're supposed to
be using those high 32 bits, not the ones we have in hand...

If we do need the iothread lock, we could do it the way that
io_readx() does, I guess, where we track whether we needed to
lock it or not.

thanks
-- PMM