linux-kernel - Re: [PATCH v5 00/20] KVM RISC-V Support

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Message-ID: <CAAhSdy2RC6Gw708wZs+FM56UkkyURgbupwdeTak7VcyarY9irg@mail.gmail.com>
Date:   Fri, 23 Aug 2019 16:55:34 +0530
From:   Anup Patel <anup@...infault.org>
To:     Alexander Graf <graf@...zon.com>
Cc:     Anup Patel <Anup.Patel@....com>,
        Palmer Dabbelt <palmer@...ive.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Paolo Bonzini <pbonzini@...hat.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: [PATCH v5 00/20] KVM RISC-V Support

On Fri, Aug 23, 2019 at 1:39 PM Alexander Graf <graf@...zon.com> wrote:
>
> On 22.08.19 10:42, Anup Patel wrote:
> > This series adds initial KVM RISC-V support. Currently, we are able to boot
> > RISC-V 64bit Linux Guests with multiple VCPUs.
> >
> > Few key aspects of KVM RISC-V added by this series are:
> > 1. Minimal possible KVM world-switch which touches only GPRs and few CSRs.
> > 2. Full Guest/VM switch is done via vcpu_get/vcpu_put infrastructure.
> > 3. KVM ONE_REG interface for VCPU register access from user-space.
> > 4. PLIC emulation is done in user-space. In-kernel PLIC emulation, will
> >     be added in future.
> > 5. Timer and IPI emuation is done in-kernel.
> > 6. MMU notifiers supported.
> > 7. FP lazy save/restore supported.
> > 8. SBI v0.1 emulation for KVM Guest available.
> >
> > Here's a brief TODO list which we will work upon after this series:
> > 1. Handle trap from unpriv access in reading Guest instruction
> > 2. Handle trap from unpriv access in SBI v0.1 emulation
> > 3. Implement recursive stage2 page table programing
> > 4. SBI v0.2 emulation in-kernel
> > 5. SBI v0.2 hart hotplug emulation in-kernel
> > 6. In-kernel PLIC emulation
> > 7. ..... and more .....
>
> Please consider patches I did not comment on as
>
> Reviewed-by: Alexander Graf <graf@...zon.com>
>
> Overall, I'm quite happy with the code. It's a very clean implementation
> of a KVM target.

Thanks Alex.

>
> The only major nit I have is the guest address space read: I don't think
> we should pull in code that we know allows user space to DOS the kernel.
> For that, we need to find an alternative. Either you implement a
> software page table walker and resolve VAs manually or you find a way to
> ensure that *any* exception taken during the read does not affect
> general code execution.

I will send v6 next week. I will try my best to implement unpriv trap
handling in v6 itself.

Regards,
Anup

>
>
> Thanks,
>
> Alex