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Date:   Thu, 8 Apr 2021 16:30:18 +0000
From:   Wei Liu <wei.liu@kernel.org>
To:     Siddharth Chandrasekaran <sidcha@amazon.de>
Cc:     Paolo Bonzini <pbonzini@redhat.com>, Wei Liu <wei.liu@kernel.org>,
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        graf@amazon.com, eyakovl@amazon.de, linux-hyperv@vger.kernel.org,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Subject: Re: [PATCH 0/4] Add support for XMM fast hypercalls
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On Thu, Apr 08, 2021 at 05:54:43PM +0200, Siddharth Chandrasekaran wrote:
> On Thu, Apr 08, 2021 at 05:48:19PM +0200, Paolo Bonzini wrote:
> > On 08/04/21 17:40, Siddharth Chandrasekaran 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.
> > > The guest is at fault here as it expects Hyper-V to consume arguments
> > > from XMM registers for certain hypercalls (that we are working) even if
> > > we didn't expose the feature via CPUID bits.
> >
> > What guest is that?
> 
> It is a Windows Server 2016.

Can you be more specific? Are you implementing some hypercalls from
TLFS? If so, which ones?

Wei.