On Wed, May 19, 2021 at 07:21:54AM +0200, Greg Kroah-Hartman wrote:

On Wed, May 19, 2021 at 10:40:13AM +0530, Anup Patel wrote:

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On Wed, May 19, 2021 at 10:28 AM Greg Kroah-Hartman
[off-list ref] wrote:

quoted

On Wed, May 19, 2021 at 09:05:35AM +0530, Anup Patel wrote:

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From: Anup Patel <anup@brainfault.org>

This series adds initial KVM RISC-V support. Currently, we are able to boot
Linux on RV64/RV32 Guest with multiple VCPUs.

Key aspects of KVM RISC-V added by this series are:
1. No RISC-V specific KVM IOCTL
2. Minimal possible KVM world-switch which touches only GPRs and few CSRs
3. Both RV64 and RV32 host supported
4. Full Guest/VM switch is done via vcpu_get/vcpu_put infrastructure
5. KVM ONE_REG interface for VCPU register access from user-space
6. PLIC emulation is done in user-space
7. Timer and IPI emuation is done in-kernel
8. Both Sv39x4 and Sv48x4 supported for RV64 host
9. MMU notifiers supported
10. Generic dirtylog supported
11. FP lazy save/restore supported
12. SBI v0.1 emulation for KVM Guest available
13. Forward unhandled SBI calls to KVM userspace
14. Hugepage support for Guest/VM
15. IOEVENTFD support for Vhost

Here's a brief TODO list which we will work upon after this series:
1. SBI v0.2 emulation in-kernel
2. SBI v0.2 hart state management emulation in-kernel
3. In-kernel PLIC emulation
4. ..... and more .....

This series can be found in riscv_kvm_v18 branch at:
https//github.com/avpatel/linux.git

Our work-in-progress KVMTOOL RISC-V port can be found in riscv_v7 branch
at: https//github.com/avpatel/kvmtool.git

The QEMU RISC-V hypervisor emulation is done by Alistair and is available
in master branch at: https://git.qemu.org/git/qemu.git

To play around with KVM RISC-V, refer KVM RISC-V wiki at:
https://github.com/kvm-riscv/howto/wiki
https://github.com/kvm-riscv/howto/wiki/KVM-RISCV64-on-QEMU
https://github.com/kvm-riscv/howto/wiki/KVM-RISCV64-on-Spike

Changes since v17:
 - Rebased on Linux-5.13-rc2
 - Moved to new KVM MMU notifier APIs
 - Removed redundant kvm_arch_vcpu_uninit()
 - Moved KVM RISC-V sources to drivers/staging for compliance with
   Linux RISC-V patch acceptance policy

What is this new "patch acceptance policy" and what does it have to do
with drivers/staging?

The Linux RISC-V patch acceptance policy is here:
Documentation/riscv/patch-acceptance.rst

As-per this policy, the Linux RISC-V maintainers will only accept
patches for frozen/ratified RISC-V extensions. Basically, it links the
Linux RISC-V development process with the RISC-V foundation
process which is painfully slow.

The KVM RISC-V patches have been sitting on the lists for almost
2 years now. The requirements for freezing RISC-V H-extension
(hypervisor extension) keeps changing and we are not clear when
it will be frozen. In fact, quite a few people have already implemented
RISC-V H-extension in hardware as well and KVM RISC-V works
on real HW as well.

Rationale of moving KVM RISC-V to drivers/staging is to continue
KVM RISC-V development without breaking the Linux RISC-V patch
acceptance policy until RISC-V H-extension is frozen. Once, RISC-V
H-extension is frozen we will move KVM RISC-V back to arch/riscv
(like other architectures).

Wait, no, this has nothing to do with what drivers/staging/ is for and
how it is used.  Again, not ok.

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What does drivers/staging/ have to do with this at all?  Did anyone ask
the staging maintainer about this?

Yes, Paolo (KVM maintainer) suggested having KVM RISC-V under
drivers/staging until RISC-V H-extension is frozen and continue the
KVM RISC-V development from there.

staging is not for stuff like this at all.  It is for code that is
self-contained (not this) and needs work to get merged into the main
part of the kernel (listed in a TODO file, and is not this).

It is not a dumping ground for stuff that arch maintainers can not seem
to agree on, and it is not a place where you can just randomly play
around with user/kernel apis with no consequences.

So no, sorry, not going to take this code at all.

And to be a bit more clear about this, having other subsystem
maintainers drop their unwanted code on this subsystem, _without_ even
asking me first is just not very nice.  All of a sudden I am now
responsible for this stuff, without me even being asked about it.
Should I start throwing random drivers into the kvm subsystem for them
to maintain because I don't want to?  :)

If there's really no other way to do this, than to put it in staging,
let's talk about it.  But saying "this must go here" is not a
conversation...

thanks,

greg k-h