linux-kernel - Re: [PATCH v5 2/8] arm64: hyperv: Add hypercall and register access functions

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Message-ID: <8cdc86e5bcf861c74069e0d349910c94@www.loen.fr>
Date:   Wed, 06 Nov 2019 11:28:30 +0109
From:   Marc Zyngier <maz@...nel.org>
To:     Michael Kelley <mikelley@...rosoft.com>
Cc:     <will@...nel.org>, <catalin.marinas@....com>,
        <mark.rutland@....com>, <linux-arm-kernel@...ts.infradead.org>,
        <gregkh@...uxfoundation.org>, <linux-kernel@...r.kernel.org>,
        <linux-hyperv@...r.kernel.org>, <devel@...uxdriverproject.org>,
        <olaf@...fle.de>, <apw@...onical.com>,
        vkuznets <vkuznets@...hat.com>, <jasowang@...hat.com>,
        <marcelo.cerri@...onical.com>, KY Srinivasan <kys@...rosoft.com>,
        Sunil Muthuswamy <sunilmut@...rosoft.com>,
        "boqun.feng" <boqun.feng@...il.com>
Subject: Re: [PATCH v5 2/8] arm64: hyperv: Add hypercall and register access  functions

On 2019-10-03 20:12, Michael Kelley wrote:
> Add ARM64-specific code to make Hyper-V hypercalls and to
> access virtual processor synthetic registers via hypercalls.
> Hypercalls use a Hyper-V specific calling sequence with a non-zero
> immediate value per Section 2.9 of the SMC Calling Convention
> spec.

I find this "following the spec by actively sidestepping it" counter
productive. You (or rather the Hyper-V people) are reinventing the
wheel (of the slightly square variety) instead of using the standard
that the whole of the ARM ecosystem seems happy to take advantage
of.

I wonder what is the rational for this. If something doesn't quite
work for Hyper-V, I think we'd all like to know.

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...