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Date:   Wed, 2 Dec 2020 14:37:16 +0100
From:   Andrea Parri <parri.andrea@gmail.com>
To:     Wei Liu <wei.liu@kernel.org>
Cc:     linux-kernel@vger.kernel.org, linux-hyperv@vger.kernel.org,
        "K . Y . Srinivasan" <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        Michael Kelley <mikelley@microsoft.com>,
        Juan Vazquez <juvazq@microsoft.com>,
        Saruhan Karademir <skarade@microsoft.com>
Subject: Re: [PATCH v2 2/7] Drivers: hv: vmbus: Avoid double fetch of msgtype
 in vmbus_on_msg_dpc()
Message-ID: <20201202133716.GA22763@andrea>
References: <20201202092214.13520-1-parri.andrea@gmail.com>
 <20201202092214.13520-3-parri.andrea@gmail.com>
 <20201202122254.zjhu3cfcq3zwvmvu@liuwe-devbox-debian-v2>
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> > @@ -1072,12 +1073,19 @@ void vmbus_on_msg_dpc(unsigned long data)
> >  		/* no msg */
> >  		return;
> >  
> > +	/*
> > +	 * The hv_message object is in memory shared with the host.  The host
> > +	 * could erroneously or maliciously modify such object.  Make sure to
> > +	 * validate its fields and avoid double fetches whenever feasible.
> > +	 */
> > +
> >  	hdr = (struct vmbus_channel_message_header *)msg->u.payload;
> > +	msgtype = hdr->msgtype;
> 
> Should READ_ONCE be used here?

I think it should.  Thank you for pointing this out.

  Andrea