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: <24726c1c-42a8-e2f2-2222-0676c8a3869f@gmail.com>
Date:   Tue, 10 May 2022 11:07:13 +0800
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101
 Thunderbird/91.9.0
Reply-To: tiala@microsoft.com
Subject: Re: [PATCH] x86/Hyper-V: Add SEV negotiate protocol support in
 Isolation VM
Content-Language: en-US
To:     Borislav Petkov <bp@alien8.de>
Cc:     kys@microsoft.com, haiyangz@microsoft.com, sthemmin@microsoft.com,
        wei.liu@kernel.org, decui@microsoft.com, tglx@linutronix.de,
        mingo@redhat.com, dave.hansen@linux.intel.com, x86@kernel.org,
        hpa@zytor.com, brijesh.singh@amd.com, venu.busireddy@oracle.com,
        michael.roth@amd.com, Tianyu.Lan@microsoft.com,
        thomas.lendacky@amd.com, jroedel@suse.de,
        michael.h.kelley@microsoft.com, linux-hyperv@vger.kernel.org,
        linux-kernel@vger.kernel.org, vkuznets@redhat.com,
        parri.andrea@gmail.com
References: <20220505131502.402259-1-ltykernel@gmail.com>
 <YnmaSB2WCJwqaZae@zn.tnic>
From:   Tianyu Lan <ltykernel@gmail.com>
Organization: Microsft
In-Reply-To: <YnmaSB2WCJwqaZae@zn.tnic>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 5/10/2022 6:48 AM, Borislav Petkov wrote:
> On Thu, May 05, 2022 at 09:15:02AM -0400, Tianyu Lan wrote:
>> From: Tianyu Lan <Tianyu.Lan@microsoft.com>
>>
>> Hyper-V Isolation VM code uses sev_es_ghcb_hv_call() to read/write MSR
>> via GHCB page. The SEV-ES guest should negotiate GHCB version before
>> reading/writing MSR via GHCB page.
> 
> Why is that?
> 
>> Expose sev_es_negotiate_protocol() and sev_es_terminate() from AMD SEV
>> code
> 
> Yeah, you keep wanting to expose random SEV-specific code and when we
> go and change it in the future, you'll come complaining that we broke
> hyperv.
> 
> I think it might be a lot better if you implement your own functions:
> for example, looking at sev_es_negotiate_protocol() - it uses only
> primitives which you can use because, well, VMGEXIT() is simply a
> wrapper around the asm insn and sev_es_wr_ghcb_msr() is simply writing
> into the MSR.
> 
> Ditto for sev_es_terminate().
> 
> And sev_es_ghcb_hv_call() too, for that matter. You can define your own.
> 
> IOW, you're much better off using those primitives and creating your own
> functions than picking out random SEV-functions and then us breaking
> your isolation VM stuff.
> 

OK. I got it. Thanks for your suggestion.