Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <f6d27366-e083-b362-b44c-eaf4d3365b53@intel.com>
Date:   Mon, 28 Nov 2022 11:48:07 -0800
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.2.2
Subject: Re: [PATCH 5/6] x86/hyperv: Support hypercalls for TDX guests
Content-Language: en-US
To:     Dexuan Cui <decui@microsoft.com>,
        "Michael Kelley (LINUX)" <mikelley@microsoft.com>,
        "ak@linux.intel.com" <ak@linux.intel.com>,
        "arnd@arndb.de" <arnd@arndb.de>, "bp@alien8.de" <bp@alien8.de>,
        "brijesh.singh@amd.com" <brijesh.singh@amd.com>,
        "Williams, Dan J" <dan.j.williams@intel.com>,
        "dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        "hpa@zytor.com" <hpa@zytor.com>,
        "jane.chu@oracle.com" <jane.chu@oracle.com>,
        "kirill.shutemov@linux.intel.com" <kirill.shutemov@linux.intel.com>,
        KY Srinivasan <kys@microsoft.com>,
        "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
        "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
        "luto@kernel.org" <luto@kernel.org>,
        "mingo@redhat.com" <mingo@redhat.com>,
        "peterz@infradead.org" <peterz@infradead.org>,
        "rostedt@goodmis.org" <rostedt@goodmis.org>,
        "sathyanarayanan.kuppuswamy@linux.intel.com" 
        <sathyanarayanan.kuppuswamy@linux.intel.com>,
        "seanjc@google.com" <seanjc@google.com>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
        "tony.luck@intel.com" <tony.luck@intel.com>,
        "wei.liu@kernel.org" <wei.liu@kernel.org>,
        "x86@kernel.org" <x86@kernel.org>
Cc:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
References: <20221121195151.21812-1-decui@microsoft.com>
 <20221121195151.21812-6-decui@microsoft.com>
 <BYAPR21MB16886270B7899F35E8A826A4D70C9@BYAPR21MB1688.namprd21.prod.outlook.com>
 <SA1PR21MB133528B2B3637D61368FF5FFBF139@SA1PR21MB1335.namprd21.prod.outlook.com>
 <b692c4da-4365-196d-9d12-33e2679c01de@intel.com>
 <SA1PR21MB1335BA9D27891F6B1BA3A988BF139@SA1PR21MB1335.namprd21.prod.outlook.com>
 <54871aec-823b-1ff5-8362-688d10e97263@intel.com>
 <SA1PR21MB13357B3CC486514D2DF50A4DBF139@SA1PR21MB1335.namprd21.prod.outlook.com>
From:   Dave Hansen <dave.hansen@intel.com>
In-Reply-To: <SA1PR21MB13357B3CC486514D2DF50A4DBF139@SA1PR21MB1335.namprd21.prod.outlook.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 11/28/22 11:37, Dexuan Cui wrote:
>> From: Dave Hansen <dave.hansen@intel.com>
...
>> How do we know, for instance, that no hypercall using this interface
>> will *ever* take the 0x0 physical address as an argument?
> 
> A 0x0 physical address as an argument still works: the 0 is passed
> to the hypervisor using GHCI. I believe Hyper-V interprets the 0 as
> an error (if the param is needed), and returns an "invalid parameter"
> error code to the guest.

I don't see any data in the public documentation to support the claim
that 0x0 is a special argument for either the input or output GPA
parameters.

This is despite some actual discussion on things like their alignment
requirements[1] and interactions with overlay pages.

So, either you are mistaken about that behavior, or it looks like the
documentation needs updating.

1.
https://learn.microsoft.com/en-us/virtualization/hyper-v-on-windows/tlfs/hypercall-interface