linux-kernel - Re: [EXTERNAL] [PATCH V2 2/9] x86/hyperv: Set Virtual Trust Level in VMBus init message

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Message-ID: <da667608-a8aa-f5b8-1621-de29b3f19272@gmail.com>
Date:   Fri, 11 Aug 2023 00:22:36 +0800
From:   Tianyu Lan <ltykernel@...il.com>
To:     Wei Liu <wei.liu@...nel.org>,
        Saurabh Singh Sengar <ssengar@...rosoft.com>
Cc:     KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Dexuan Cui <decui@...rosoft.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>,
        "daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
        "arnd@...db.de" <arnd@...db.de>,
        "Michael Kelley (LINUX)" <mikelley@...rosoft.com>,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "vkuznets@...hat.com" <vkuznets@...hat.com>
Subject: Re: [EXTERNAL] [PATCH V2 2/9] x86/hyperv: Set Virtual Trust Level in
 VMBus init message

On 8/7/2023 12:48 PM, Wei Liu wrote:
> On Fri, Jul 07, 2023 at 09:07:54AM +0000, Saurabh Singh Sengar wrote:
>>
>>
>>> +
>>> +	ret = hv_do_hypercall(control, input, output);
>>> +	if (hv_result_success(ret))
>>> +		vtl = output->as64.low & HV_X64_VTL_MASK;
>>> +	else
>>> +		pr_err("Hyper-V: failed to get VTL! %lld", ret);
>>
>> In case of error this function will return vtl=0, which can be the valid value of vtl.
>> I suggest we initialize vtl with -1 so and then check for its return.
>>
>> This could be a good utility function which can be used for any Hyper-V VTL system, so think
>> of making it global ?
>>
> 
> Tianyu -- your thought on this?

In current user cases, the guest only runs in VTL0 and Hyper-V may
return VTL error in some cases but kernel still may run with 0 as VTL.

I just sent out v5 and set VTL to 0 by default if fail to get VTL from
Hyper-V and give out a warning log. The get_vtl() is only called on 
enlightened SEV-SNP guest. If there is new case that needs handle the 
error from Hyper-V when call VTL hvcall, we may add the logic later.