linux-kernel - RE: [PATCH v4 09/15] Drivers: hv: Introduce hv_output_arg_exists in hv

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Message-ID: <PH7PR21MB3263F2F8507C8472DE00F546CEC9A@PH7PR21MB3263.namprd21.prod.outlook.com>
Date:   Fri, 6 Oct 2023 18:13:28 +0000
From:   Long Li <longli@...rosoft.com>
To:     Nuno Das Neves <nunodasneves@...ux.microsoft.com>,
        Alex Ionescu <aionescu@...il.com>,
        Dexuan Cui <decui@...rosoft.com>,
        "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
CC:     "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "patches@...ts.linux.dev" <patches@...ts.linux.dev>,
        "Michael Kelley (LINUX)" <mikelley@...rosoft.com>,
        KY Srinivasan <kys@...rosoft.com>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Dexuan Cui <decui@...rosoft.com>,
        "apais@...ux.microsoft.com" <apais@...ux.microsoft.com>,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        "ssengar@...ux.microsoft.com" <ssengar@...ux.microsoft.com>,
        MUKESH RATHOR <mukeshrathor@...rosoft.com>,
        "stanislav.kinsburskiy@...il.com" <stanislav.kinsburskiy@...il.com>,
        "jinankjain@...ux.microsoft.com" <jinankjain@...ux.microsoft.com>,
        vkuznets <vkuznets@...hat.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "will@...nel.org" <will@...nel.org>,
        "catalin.marinas@....com" <catalin.marinas@....com>
Subject: RE: [PATCH v4 09/15] Drivers: hv: Introduce hv_output_arg_exists in
 hv_common.c

> Subject: Re: [PATCH v4 09/15] Drivers: hv: Introduce hv_output_arg_exists in
> hv_common.c
> 
> On 10/2/2023 12:29 PM, Alex Ionescu wrote:
> > Hi Nuno,
> >
> > Is it possible to simply change to always allocating the output page?
> > For example, the output page could be needed in scenarios where Linux
> > is not running as the root partition, since certain hypercalls that a
> > guest can make will still require one (I realize that's not the case
> > _today_, but I don't believe this optimization buys much).
> 
> I agree - it would indeed simplify the code, and guests will probably make use of it
> sooner or later.
> 
> Happy to make that change if Hyper-V guest maintainers agree.
> Long, Dexuan, Michael, what do you think?

There is no use case as of today for guest VMs. And it allocates extra memory that are never used when running as guest VMs.

I suggest keep this code unchanged as is.

Thanks,
Long