linux-kernel - Re: [PATCH v18 00/18] KVM RISC-V Support

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Message-ID: <00d96cc3-026e-bd78-db08-f9e98a4abeff@redhat.com>
Date:   Fri, 21 May 2021 22:25:59 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Palmer Dabbelt <palmerdabbelt@...gle.com>, anup@...infault.org,
        Anup Patel <Anup.Patel@....com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        aou@...s.berkeley.edu, corbet@....net, graf@...zon.com,
        Atish Patra <Atish.Patra@....com>,
        Alistair Francis <Alistair.Francis@....com>,
        Damien Le Moal <Damien.LeMoal@....com>, kvm@...r.kernel.org,
        kvm-riscv@...ts.infradead.org, linux-riscv@...ts.infradead.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-staging@...ts.linux.dev
Subject: Re: [PATCH v18 00/18] KVM RISC-V Support

On 21/05/21 19:47, Greg KH wrote:
> If this isn't in any hardware that anyone outside of
> internal-to-company-prototypes, then let's wait until it really is in a
> device that people can test this code on.
> 
> What's the rush to get this merged now if no one can use it?

There is not just hardware, there are simulators and emulators too (you 
can use QEMU to test it for example), and it's not exactly a rush since 
it's basically been ready for 2 years and has hardly seen any code 
changes since v13 which was based on Linux 5.9.

Not having the code upstream is hindering further development so that 
RISC-V KVM can be feature complete when hardware does come out.  Missing 
features and optimizations could be added on top, but they are harder to 
review if they are integrated in a relatively large series instead of 
being done incrementally.  Not having the header files in Linus's tree 
makes it harder to merge RISC-V KVM support in userspace (userspace is 
shielded anyway by any future changes to the hypervisor specification, 
so there's no risk of breaking the ABI).

At some point one has to say enough is enough; for me, that is after one 
year with no changes to the spec and, especially, no deadline in sight 
for freezing it.  The last 5 versions of the patch set were just 
adapting to changes in the generic KVM code.  If the code is good, I 
don't see why the onus of doing those changes should be on Anup, rather 
than being shared amongst all KVM developers as is the case for all the 
other architectures.

Paolo