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Subject: Re: [PATCH] asm-generic/hyperv: Fix struct hv_message_header ordering
Date:   Thu, 29 Jul 2021 16:26:54 +0200
From:   Siddharth Chandrasekaran <sidcha@amazon.de>
To:     Wei Liu <wei.liu@kernel.org>
CC:     Vitaly Kuznetsov <vkuznets@redhat.com>,
        Siddharth Chandrasekaran <sidcha.dev@gmail.com>,
        Liran Alon <liran@amazon.com>,
        Ioannis Aslanidis <iaslan@amazon.de>,
        <linux-hyperv@vger.kernel.org>, <linux-arch@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>,
        "K. Y. Srinivasan" <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        Dexuan Cui <decui@microsoft.com>, Arnd Bergmann <arnd@arndb.de>
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References: <20210729133702.11383-1-sidcha@amazon.de>
 <87eebh9qhd.fsf@vitty.brq.redhat.com>
 <20210729140705.wj5tokeq6lkxm2yy@liuwe-devbox-debian-v2>
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On Thu, Jul 29, 2021 at 02:07:05PM +0000, Wei Liu wrote:
> On Thu, Jul 29, 2021 at 03:52:46PM +0200, Vitaly Kuznetsov wrote:
> > Siddharth Chandrasekaran <sidcha@amazon.de> writes:
> >
> > > According to Hyper-V TLFS Version 6.0b, struct hv_message_header members
> > > should be defined in the order:
> > >
> > >     message_type, reserved, message_flags, payload_size
> > >
> > > but we have it defined in the order:
> > >
> > >     message_type, payload_size, message_flags, reserved
> > >
> > > that is, the payload_size and reserved members swapped.
> >
> > Indeed,
> >
> > typedef struct
> > {
> >       HV_MESSAGE_TYPE MessageType;
> >       UINT16 Reserved;
> >       HV_MESSAGE_FLAGS MessageFlags;
> >       UINT8 PayloadSize;
> >       union
> >       {
> >               UINT64 OriginationId;
> >               HV_PARTITION_ID Sender;
> >               HV_PORT_ID Port;
> >       };
> > } HV_MESSAGE_HEADER;
> 
> Well. I think TLFS is wrong. Let me ask around.

TBH, I hadn't considered that possibility :). I assumed it was a
regression on our side. But I spent some time tracing the history of that
struct all the way back to when it was in staging (in 2009) and now I'm
inclined to believe a later version of TLFS is at fault here.

Based on what we decide in this thread, I will open an issue on the TLFS
GitHub repository.

~ Sid.


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