On 2020-02-19 15:46, Jan Kiszka wrote:
On 19.02.20 16:09, Arnd Bergmann wrote:
On Mon, Feb 10, 2020 at 3:13 PM Marc Zyngier <maz@xxxxxxxxxx> wrote:
KVM/arm was merged just over 7 years ago, and has lived a very quiet
life so far. It mostly works if you're prepared to deal with its
limitations, it has been a good prototype for the arm64 version,
but it suffers a few problems:
- It is incomplete (no debug support, no PMU)
- It hasn't followed any of the architectural evolutions
- It has zero users (I don't count myself here)
- It is more and more getting in the way of new arm64 developments
So here it is: unless someone screams and shows that they rely on
KVM/arm to be maintained upsteam, I'll remove 32bit host support
form the tree. One of the reasons that makes me confident nobody is
using it is that I never receive *any* bug report. Yes, it is
perfect.
But if you depend on KVM/arm being available in mainline, please
shout.
To reiterate: 32bit guest support for arm64 stays, of course. Only
32bit host goes. Once this is merged, I plan to move virt/kvm/arm to
arm64, and cleanup all the now unnecessary abstractions.
The patches have been generated with the -D option to avoid spamming
everyone with huge diffs, and there is a kvm-arm/goodbye branch in
my kernel.org repository.
Just one more thought before it's gone: is there any shared code
(header files?) that is used by the jailhouse hypervisor?
If there is, are there any plans to merge that into the mainline
kernel
for arm32 in the near future?
I'm guessing the answer to at least one of those questions is 'no', so
we don't need to worry about it, but it seems better to ask.
Good that you mention it: There is one thing we share on ARM (and
ARM64), and that is the hypervisor enabling stub, to install our own
vectors. If that was to be removed as well, we would have to patch it
back downstream. So far, we only carry few EXPORT_SYMBOL patches for
essential enabling.
I actually have a few extra patches on top of the series, one of them
actually removing the ability to register new vectors (mostly because
I don't like leaving unused stuff behind), see [1]. I'll post an update
so that we can discuss whether we want this particular to stay or not.
That said, I was also starting to think about how long we will
continue to support Jailhouse on 32-bit ARM. We currently have no
supported SoC there that comes with an SMMU, and I doubt to see one
still showing up. So, Jailhouse on ARM is really just a testing/demo
case, maybe useful (but I didn't get concrete feedback) for cleaner
collaborative AMP for real-time purposes, without security concerns. I
assume 32-bit ARM will never be part of what would be proposed of
Jailhouse for upstream.
I guess we all come to the same conclusion...
M.
[1]
https://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git/commit/?h=kvm-arm/goodbye&id=0943dd119105b65197adffda52c402cce28da56d
--
Jazz is not dead. It just smells funny...
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