linux-kernel - Re: [PATCH] x86/hyper-v: define structures from TLFS as packed

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Message-ID: <87y39awwzz.fsf@vitty.brq.redhat.com>
Date:   Fri, 30 Nov 2018 13:49:52 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        linux-kernel@...r.kernel.org, Roman Kagan <rkagan@...tuozzo.com>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>, x86@...nel.org,
        "Michael Kelley \(EOSG\)" <Michael.H.Kelley@...rosoft.com>,
        Nadav Amit <nadav.amit@...il.com>
Subject: Re: [PATCH] x86/hyper-v: define structures from TLFS as packed

Thomas Gleixner <tglx@...utronix.de> writes:

> On Fri, 30 Nov 2018, Vitaly Kuznetsov wrote:
>
>> Subject: x86/hyper-v: define structures from TLFS as packed
>
> Please start the first word after the prefix colon with an uppercase
> letter. Also structures from TLFS doesn't make sense to me. Something like
> this:
>
> Subject: x86/hyper-v: Mark TLFS structures packed
>
>> Without 'packed' compiler is free to add optimization paddings and re-order
>> structure fields for randomization/optimization. And structures from
>
> s/And/As/ ?
>
>> hyperv-tlfs.h are used for hypervisor-guest communication, we need to
>> ultimately forbid such practices.
>
> That whole paragraph reads a bit strange. Something like:
>
>   The TLFS structures are used for hypervisor-guest communication and must
>   exactly meet the specification.
>
>   Compilers can add alignment padding to structures or reorder struct
>   members for randomization and optimization, which would break the
>   hypervisor ABI.
>
>   Mark the structures as packed to prevent this.
>
> Hmm?

Sure, will do v2!

>
>> Suggested-by: Nadav Amit <nadav.amit@...il.com>
>> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
>
> Other than that: Acked-by: Thomas Gleixner <tglx@...utronix.de>

Thanks!

-- 
Vitaly