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

From: Anup Patel <anup@brainfault.org>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Damien Le Moal <Damien.LeMoal@wdc.com>,
	Palmer Dabbelt <palmer@sifive.com>,
	Daniel Lezcano <daniel.lezcano@linaro.org>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	Radim K <rkrcmar@redhat.com>, Anup Patel <Anup.Patel@wdc.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Christoph Hellwig <hch@infradead.org>,
	Atish Patra <Atish.Patra@wdc.com>,
	Alistair Francis <Alistair.Francis@wdc.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	"linux-riscv@lists.infradead.org"
	<linux-riscv@lists.infradead.org>
Subject: Re: [RFC PATCH 00/16] KVM RISC-V Support
Date: Tue, 30 Jul 2019 19:20:15 +0530	[thread overview]
Message-ID: <CAAhSdy0Sy9YV5ymdFk0URLY4GvOkWaWOpC_Dju+1ada_yc=Pmw@mail.gmail.com> (raw)
In-Reply-To: <965cffdb-86e2-b422-9c23-345c7100fd88@redhat.com>

On Tue, Jul 30, 2019 at 5:03 PM Paolo Bonzini <pbonzini@redhat.com> wrote:
>
> 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. :)

Thanks, your review comments are very useful. We will address all
of them.

>
> 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

I thought VHOST requires irqfd and we would certainly endup providing
in-kernel PLIC emulation to support VHOST.

> 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).

The get/putchar SBI v0.1 calls won't be encouraged going forward because
we already have earlycon implmentation in-place and Guest kernel can directly
write to UART registers for earlyprints.

If we still wanted to implement get/putchar calls then we would need a RISC-V
specific exit reason in KVM. We have tried to avoid RISC-V specific IOCTLs
or exit reason in this series.

>
> > 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.
>

Thanks,
Anup

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