linux-kernel - Re: [PATCH 0/4] Add support for XMM fast hypercalls

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Date:   Thu, 8 Apr 2021 15:38:13 +0000
From:   Wei Liu <wei.liu@...nel.org>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Wei Liu <wei.liu@...nel.org>,
        Siddharth Chandrasekaran <sidcha@...zon.de>, kys@...rosoft.com,
        haiyangz@...rosoft.com, sthemmin@...rosoft.com, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, x86@...nel.org, hpa@...or.com,
        seanjc@...gle.com, vkuznets@...hat.com, wanpengli@...cent.com,
        jmattson@...gle.com, joro@...tes.org, graf@...zon.com,
        eyakovl@...zon.de, linux-hyperv@...r.kernel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH 0/4] Add support for XMM fast hypercalls

On Thu, Apr 08, 2021 at 05:30:26PM +0200, Paolo Bonzini wrote:
> On 08/04/21 17:28, Wei Liu wrote:
> > > Although the Hyper-v TLFS mentions that a guest cannot use this feature
> > > unless the hypervisor advertises support for it, some hypercalls which
> > > we plan on upstreaming in future uses them anyway.
> > 
> > No, please don't do this. Check the feature bit(s) before you issue
> > hypercalls which rely on the extended interface.
> 
> Perhaps Siddharth should clarify this, but I read it as Hyper-V being buggy
> and using XMM arguments unconditionally.
> 

There is no code in upstream Linux that uses the XMM fast hypercall
interface at the moment.

If there is such code, it has bugs in it and should be fixed. :-)

Wei.

> Paolo
>