svn commit: r307626 - head/sys/ufs/ffs

[Adrian Chadd]

Ok, so after talking with others, my questions are:

* I thought our VM was supposed to not be doing double mapping like
this. warner's comment on irc was:

===
13:39 < bsdimp> adrian the VM isn't supposed to do it at all.
13:39 < bsdimp> adrian that is, double map on purpose.
13:40 < bsdimp> though there's some exceptions to the rule
13:40 < bsdimp> since kernel mappings go away in userland, and
userland doesn't execute while you're in kernel mode, you can do the
flushing
                game in busdma to prevent most issues.
13:41 < bsdimp> which is what we do. Generally, though, our VM doesn't
do it in-kernel.
===

* is this still the case? or are there places in the VM where we are doing this?
* can we introduce a machdep/pmap capability check to see if aliasing
is allowed and if so, turn this feature on?

Adding a pmap capability and turning it on for say, i386/amd64/arm64
would allow for this new feature as well as the previous behaviour on
older platforms.

I don't think I have the time to fix mips pmap to support this new
feature, so if you want to turn it on for all features, we should
really fix/test pmap on said platforms first.

Final comment: I'd really like to see a sort of "tested on" for things
like this, because it's not clear which platforms/architectures it was
tested on.

Thanks,



-adrian