linux-kernel - Re: [PATCH v6 10/21] RISC-V: KVM: Handle MMIO exits for VCPU

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Date:   Tue, 3 Sep 2019 10:58:23 +0200
From:   Andrew Jones <drjones@...hat.com>
To:     Anup Patel <Anup.Patel@....com>
Cc:     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>,
        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 v6 10/21] RISC-V: KVM: Handle MMIO exits for VCPU

On Thu, Aug 29, 2019 at 01:56:18PM +0000, Anup Patel wrote:
>  int kvm_riscv_vcpu_mmio_return(struct kvm_vcpu *vcpu, struct kvm_run *run)
>  {
> -	/* TODO: */
> +	u8 data8;
> +	u16 data16;
> +	u32 data32;
> +	u64 data64;
> +	ulong insn;
> +	int len, shift;
> +
> +	insn = vcpu->arch.mmio_decode.insn;
> +
> +	if (run->mmio.is_write)
> +		goto done;
> +
> +	len = vcpu->arch.mmio_decode.len;
> +	shift = vcpu->arch.mmio_decode.shift;
> +
> +	switch (len) {
> +	case 1:
> +		data8 = *((u8 *)run->mmio.data);
> +		SET_RD(insn, &vcpu->arch.guest_context,
> +			(ulong)data8 << shift >> shift);
> +		break;
> +	case 2:
> +		data16 = *((u16 *)run->mmio.data);
> +		SET_RD(insn, &vcpu->arch.guest_context,
> +			(ulong)data16 << shift >> shift);
> +		break;
> +	case 4:
> +		data32 = *((u32 *)run->mmio.data);
> +		SET_RD(insn, &vcpu->arch.guest_context,
> +			(ulong)data32 << shift >> shift);
> +		break;
> +	case 8:
> +		data64 = *((u64 *)run->mmio.data);
> +		SET_RD(insn, &vcpu->arch.guest_context,
> +			(ulong)data64 << shift >> shift);
> +		break;
> +	default:
> +		return -ENOTSUPP;
> +	};
> +
> +done:
> +	/* Move to next instruction */
> +	vcpu->arch.guest_context.sepc += INSN_LEN(insn);
> +

As I pointed out in the last review, just moving this instruction skip
here is not enough. Doing so introduces the same problem that 2113c5f62b74
("KVM: arm/arm64: Only skip MMIO insn once") fixes for arm.

Thanks,
drew