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Date:   Wed, 29 Aug 2018 17:14:33 +0200
From:   Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>
To:     Peng Hao <peng.hao2@zte.com.cn>
Cc:     pbonzini@redhat.com, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org, zhong.weidong@zte.com.cn,
        wanpeng.li@hotmail.com
Subject: Re: [PATCH V3 1/2] kvm/x86 : add coalesced pio support
Message-ID: <20180829151432.GA19487@flask>
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2018-08-24 19:20+0800, Peng Hao:
> Signed-off-by: Peng Hao <peng.hao2@zte.com.cn>
> ---
>  include/uapi/linux/kvm.h  | 5 +++--
>  virt/kvm/coalesced_mmio.c | 8 +++++---
>  virt/kvm/kvm_main.c       | 2 ++
>  3 files changed, 10 insertions(+), 5 deletions(-)
> 
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index b6270a3..9cc56d3 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -420,13 +420,13 @@ struct kvm_run {
>  struct kvm_coalesced_mmio_zone {
>  	__u64 addr;
>  	__u32 size;
> -	__u32 pad;
> +	__u32 pio;

I would prefer to have this as a slightly more compatible

	union {
		__u32 pad;
		__u32 pio;
	};

>  };
>  
>  struct kvm_coalesced_mmio {
>  	__u64 phys_addr;
>  	__u32 len;
> -	__u32 pad;
> +	__u32 pio;

Also, please add a check that "pio <= 1".

This would catch most cases where userspace passed garbage in that field
and we'd also make the remaining bits available for future features.

Thanks.