linux-kernel - Re: [PATCH v7 10/21] RISC-V: KVM: Handle MMIO exits for VCPU

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Message-ID: <f5bf0227-5066-5fcc-55bd-9a3777826404@amazon.com>
Date:   Mon, 23 Sep 2019 08:50:27 +0200
From:   Alexander Graf <graf@...zon.com>
To:     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>
CC:     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>,
        Anup Patel <anup@...infault.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 v7 10/21] RISC-V: KVM: Handle MMIO exits for VCPU



On 04.09.19 18:15, Anup Patel wrote:
> We will get stage2 page faults whenever Guest/VM access SW emulated
> MMIO device or unmapped Guest RAM.
> 
> This patch implements MMIO read/write emulation by extracting MMIO
> details from the trapped load/store instruction and forwarding the
> MMIO read/write to user-space. The actual MMIO emulation will happen
> in user-space and KVM kernel module will only take care of register
> updates before resuming the trapped VCPU.
> 
> The handling for stage2 page faults for unmapped Guest RAM will be
> implemeted by a separate patch later.
> 
> Signed-off-by: Anup Patel <anup.patel@....com>
> Acked-by: Paolo Bonzini <pbonzini@...hat.com>
> Reviewed-by: Paolo Bonzini <pbonzini@...hat.com>

This version is indeed much better. I would not mind a bit more 
documentation when it comes to implicit register value assumptions (a0, 
a1 in the trap handler), but the code is small enough that someone who 
cares can figure it out quickly enough.

Reviewed-by: Alexander Graf <graf@...zon.com>


Alex



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