linux-kernel - Re: [RFC PATCH 00/16] KVM RISC-V Support

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Message-ID: <965cffdb-86e2-b422-9c23-345c7100fd88@redhat.com>
Date:   Tue, 30 Jul 2019 13:33:08 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Anup Patel <anup@...infault.org>
Cc:     Anup Patel <Anup.Patel@....com>,
        Palmer Dabbelt <palmer@...ive.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Radim K <rkrcmar@...hat.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Atish Patra <Atish.Patra@....com>,
        Alistair Francis <Alistair.Francis@....com>,
        Damien Le Moal <Damien.LeMoal@....com>,
        Christoph Hellwig <hch@...radead.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 00/16] KVM RISC-V Support

On 30/07/19 07:26, Anup Patel wrote:
> Here's a brief TODO list which we want to immediately work upon after this
> series:
> 1. Handle trap from unpriv access in SBI v0.1 emulation
> 2. In-kernel PLIC emulation
> 3. SBI v0.2 emulation in-kernel
> 4. SBI v0.2 hart hotplug emulation in-kernel
> 5. ..... and so on .....
> 
> We will include above TODO list in v2 series cover letter as well.

I guess I gave you a bunch of extra items in today's more thorough
review. :)

BTW, since IPIs are handled in the SBI I wouldn't bother with in-kernel
PLIC emulation unless you can demonstrate performance improvements (for
example due to irqfd).  In fact, it may be more interesting to add
plumbing for userspace handling of selected SBI calls (in addition to
get/putchar, sbi_system_reset and sbi_hart_down look like good
candidates in SBI v0.2).

> We were thinking to keep KVM RISC-V disabled by default (i.e. keep it
> experimental) until we have validated it on some FPGA or real HW. For now,
> users can explicitly enable it and play-around on QEMU emulation. I hope
> this is fine with most people ?

That's certainly okay with me.

Paolo