Re: [Qemu-devel] [PATCH v2 10/45] translate-all: guarantee that tb_hash only holds valid TBs

[Emilio G. Cota]

On Mon, Jul 17, 2017 at 19:29:57 -1000, Richard Henderson wrote:
> On 07/17/2017 06:54 PM, Emilio G. Cota wrote:
> >What threw me off was that in lookup_tb_ptr we're not checking tb->invalid,
> >and that biased me into thinking that it's not needed. But I should have
> >tried harder. Also, that's a bug, and yet another reason to have tb_lookup,
> >so that we fix these things at once in one place.
> 
> Yes, me as well.  Quite right we need only one copy of this code.
> 
> >>         (tb->flags & (CF_HASH_MASK | CF_INVALID)) == cf_mask
> >>
> >>So that we continue to check CF_INVALID each time we lookup a TB, but now we
> >>get it for free as a part of the other flags check.
> >
> >With the annoying atomic_read thrown in there :-) but yes, will do.
> 
> Yes of course.  ;-)

Gaah, we'll need to update all readers of tb->cflags, of which we have
plenty (~145, mostly in target code) to avoid C11 undefined behaviour
and make Paolo happy.

Should I do those updates in the same patch where tb->invalid is brought
over to cflags? Alternatives: have a later patch where all readers
are converted to atomic_read, or keep tb->invalid as a separate field (we
could use that 4-byte hole in struct tb_tc..)

                E.