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([2001:b07:6468:f312:5e2c:eb9a:a8b6:fd3e]) by smtp.gmail.com with ESMTPSA id o17sm10489411edt.10.2021.04.08.08.48.19 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 08 Apr 2021 08:48:20 -0700 (PDT) Subject: Re: [PATCH 0/4] Add support for XMM fast hypercalls To: Siddharth Chandrasekaran Cc: Wei Liu , kys@microsoft.com, haiyangz@microsoft.com, sthemmin@microsoft.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com, seanjc@google.com, vkuznets@redhat.com, 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> <033e7d77-d640-2c12-4918-da6b5b7f4e21@redhat.com> <20210408154006.GA32315@u366d62d47e3651.ant.amazon.com> From: Paolo Bonzini Message-ID: <53200f24-bd57-1509-aee2-0723aa8a3f6f@redhat.com> Date: Thu, 8 Apr 2021 17:48:19 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0 MIME-Version: 1.0 In-Reply-To: <20210408154006.GA32315@u366d62d47e3651.ant.amazon.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? Paolo