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

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Message-ID: <757C929B-D26C-46D9-98E8-1191E3B86F3C@amazon.com>
Date:   Fri, 23 Aug 2019 11:44:43 +0000
From:   "Graf (AWS), Alexander" <graf@...zon.com>
To:     Anup Patel <anup@...infault.org>
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



> Am 23.08.2019 um 13:26 schrieb Anup Patel <anup@...infault.org>:
> 
>> 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.

Are you sure unpriv is the only exception that can hit there? What about NMIs? Do you have #MCs yet (ECC errors)? Do you have something like ARM's #SError which can asynchronously hit at any time because of external bus (PCI) errors?

Alex

> 
> Regards,
> Anup
> 
>> 
>> 
>> Thanks,
>> 
>> Alex