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Subject: Re: [PATCH 0/4] Add support for XMM fast hypercalls
To:     Wei Liu <wei.liu@kernel.org>,
        Siddharth Chandrasekaran <sidcha@amazon.de>
Cc:     kys@microsoft.com, haiyangz@microsoft.com, sthemmin@microsoft.com,
        tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, x86@kernel.org,
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        wanpengli@tencent.com, jmattson@google.com, joro@8bytes.org,
        graf@amazon.com, eyakovl@amazon.de, linux-hyperv@vger.kernel.org,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org
References: <20210407212926.3016-1-sidcha@amazon.de>
 <20210408152817.k4d4hjdqu7hsjllo@liuwe-devbox-debian-v2>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <033e7d77-d640-2c12-4918-da6b5b7f4e21@redhat.com>
Date:   Thu, 8 Apr 2021 17:30:26 +0200
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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.

Paolo