Re: [RFC PATCH 00/12] Ion cleanup in preparation for moving out of staging

From: Brian Starkey
Date: Mon Mar 13 2017 - 06:54:56 EST

On Sun, Mar 12, 2017 at 02:34:14PM +0100, Benjamin Gaignard wrote:
2017-03-09 18:38 GMT+01:00 Laura Abbott <labbott@xxxxxxxxxx>:
On 03/09/2017 02:00 AM, Benjamin Gaignard wrote:
2017-03-06 17:04 GMT+01:00 Daniel Vetter <daniel@xxxxxxxx>:
On Mon, Mar 06, 2017 at 11:58:05AM +0100, Mark Brown wrote:
On Mon, Mar 06, 2017 at 11:40:41AM +0100, Daniel Vetter wrote:

No one gave a thing about android in upstream, so Greg KH just dumped it
all into staging/android/. We've discussed ION a bunch of times, recorded
anything we'd like to fix in staging/android/TODO, and Laura's patch
series here addresses a big chunk of that.

This is pretty much the same approach we (gpu folks) used to de-stage the
syncpt stuff.

Well, there's also the fact that quite a few people have issues with the
design (like Laurent). It seems like a lot of them have either got more
comfortable with it over time, or at least not managed to come up with
any better ideas in the meantime.

See the TODO, it has everything a really big group (look at the patch for
the full Cc: list) figured needs to be improved at LPC 2015. We don't just
merge stuff because merging stuff is fun :-)

Laurent was even in that group ...

For me those patches are going in the right direction.

I still have few questions:
- since alignment management has been remove from ion-core, should it
be also removed from ioctl structure ?

Yes, I think I'm going to go with the suggestion to fixup the ABI
so we don't need the compat layer and as part of that I'm also
dropping the align argument.

- can you we ride off ion_handle (at least in userland) and only
export a dma-buf descriptor ?

Yes, I think this is the right direction given we're breaking
everything anyway. I was debating trying to keep the two but
moving to only dma bufs is probably cleaner. The only reason
I could see for keeping the handles is running out of file
descriptors for dma-bufs but that seems unlikely.

In the future how can we add new heaps ?
Some platforms have very specific memory allocation
requirements (just have a look in the number of gem custom allocator in drm)
Do you plan to add heap type/mask for each ?

Yes, that was my thinking.

My concern is about the policy to adding heaps, will you accept
"customs" heap per
platforms ? per devices ? or only generic ones ?
If you are too strict, we will have lot of out-of-tree heaps and if
you accept of of them
it will be a nightmare to maintain....

Are you concerned about actual heaps (e.g. a carveout at 0x80000000 vs
a carveout at 0x60000000) or heap types?

For heap types, I think the policy can be strict - if it's generally
useful then it should live in-tree in ion. Otherwise, it would be
out-of-tree. I'd expect most "custom" heaps to be parameterisable to
the point of being generally useful.

For actual heap instances, I would expect them to be communicated via
reserved-memory regions or something similar, and so the maintenance
burden is pretty low.

The existing query ioctl can allow heap IDs to get assigned
dynamically at runtime, so there's no need to reserve "bit 6" for

Another point is how can we put secure rules (like selinux policy) on
heaps since all the allocations
go to the same device (/dev/ion) ? For example, until now, in Android
we have to give the same
access rights to all the process that use ION.
It will become problem when we will add secure heaps because we won't
be able to distinguish secure
processes to standard ones or set specific policy per heaps.
Maybe I'm wrong here but I have never see selinux policy checking an
ioctl field but if that
exist it could be a solution.

I might be thinking of a different type of "secure", but...

Should the security of secure heaps be enforced by OS-level
permissions? I don't know about other architectures, but at least on
arm/arm64 this is enforced in hardware; it doesn't matter who has
access to the ion heap, because only secure devices (or the CPU
running a secure process) is physically able to access the memory
backing the buffer.

In fact, in the use-cases I know of, the process asking for the ion
allocation is not a secure process, and so we wouldn't *want* to
restrict the secure heap to be allocated from only by secure