Re: [PATCH 1/2] kvm/arm: skip MMIO insn after emulation

["Alex Bennée" <alex.bennee@linaro.org>]

Mark Rutland <mark.rutland@arm.com> writes:

> When we emulate an MMIO instruction, we advance the CPU state within
> decode_hsr(), before emulating the instruction effects.
>
> Having this logic in decode_hsr() is opaque, and advancing the state
> before emulation is problematic. It gets in the way of applying
> consistent single-step logic, and it prevents us from being able to fail
> an MMIO instruction with a synchronous exception.
>
> Clean this up by only advancing the CPU state *after* the effects of the
> instruction are emulated.
>
> Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> Cc: Alex Bennée <alex.bennee@linaro.org>
> Cc: Christoffer Dall <christoffer.dall@arm.com>
> Cc: Marc Zyngier <marc.zyngier@arm.com>
> Cc: Peter Maydell <peter.maydell@linaro.org>

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>

> ---
>  virt/kvm/arm/mmio.c | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/virt/kvm/arm/mmio.c b/virt/kvm/arm/mmio.c
> index dac7ceb1a677..08443a15e6be 100644
> --- a/virt/kvm/arm/mmio.c
> +++ b/virt/kvm/arm/mmio.c
> @@ -117,6 +117,12 @@ int kvm_handle_mmio_return(struct kvm_vcpu *vcpu, struct kvm_run *run)
>  		vcpu_set_reg(vcpu, vcpu->arch.mmio_decode.rt, data);
>  	}
>
> +	/*
> +	 * The MMIO instruction is emulated and should not be re-executed
> +	 * in the guest.
> +	 */
> +	kvm_skip_instr(vcpu, kvm_vcpu_trap_il_is32bit(vcpu));
> +
>  	return 0;
>  }
>
> @@ -144,11 +150,6 @@ static int decode_hsr(struct kvm_vcpu *vcpu, bool *is_write, int *len)
>  	vcpu->arch.mmio_decode.sign_extend = sign_extend;
>  	vcpu->arch.mmio_decode.rt = rt;
>
> -	/*
> -	 * The MMIO instruction is emulated and should not be re-executed
> -	 * in the guest.
> -	 */
> -	kvm_skip_instr(vcpu, kvm_vcpu_trap_il_is32bit(vcpu));
>  	return 0;
>  }


--
Alex Bennée

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