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Date:   Mon, 7 Aug 2023 04:48:27 +0000
From:   Wei Liu <wei.liu@kernel.org>
To:     Saurabh Singh Sengar <ssengar@microsoft.com>
Cc:     Tianyu Lan <ltykernel@gmail.com>,
        KY Srinivasan <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        "wei.liu@kernel.org" <wei.liu@kernel.org>,
        Dexuan Cui <decui@microsoft.com>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
        "mingo@redhat.com" <mingo@redhat.com>,
        "bp@alien8.de" <bp@alien8.de>,
        "dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
        "x86@kernel.org" <x86@kernel.org>, "hpa@zytor.com" <hpa@zytor.com>,
        "daniel.lezcano@linaro.org" <daniel.lezcano@linaro.org>,
        "arnd@arndb.de" <arnd@arndb.de>,
        "Michael Kelley (LINUX)" <mikelley@microsoft.com>,
        Tianyu Lan <Tianyu.Lan@microsoft.com>,
        "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
        "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "vkuznets@redhat.com" <vkuznets@redhat.com>
Subject: Re: [EXTERNAL] [PATCH V2 2/9] x86/hyperv: Set Virtual Trust Level in
 VMBus init message
Message-ID: <ZNB3m6Qiml7JDTQ7@liuwe-devbox-debian-v2>
References: <20230627032248.2170007-1-ltykernel@gmail.com>
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On Fri, Jul 07, 2023 at 09:07:54AM +0000, Saurabh Singh Sengar wrote:
> 
> 
[...]
> > +static u8 __init get_vtl(void)
> > +{
> > +	u64 control = HV_HYPERCALL_REP_COMP_1 |
> > HVCALL_GET_VP_REGISTERS;
> > +	struct hv_get_vp_registers_input *input;
> > +	struct hv_get_vp_registers_output *output;
> > +	u64 vtl = 0;
> > +	u64 ret;
> > +	unsigned long flags;
> > +
> > +	local_irq_save(flags);
> > +	input = *this_cpu_ptr(hyperv_pcpu_input_arg);
> > +	output = (struct hv_get_vp_registers_output *)input;
> > +	if (!input) {
> > +		local_irq_restore(flags);
> > +		goto done;
> > +	}
> > +
> > +	memset(input, 0, struct_size(input, element, 1));
> > +	input->header.partitionid = HV_PARTITION_ID_SELF;
> > +	input->header.vpindex = HV_VP_INDEX_SELF;
> > +	input->header.inputvtl = 0;
> > +	input->element[0].name0 = HV_X64_REGISTER_VSM_VP_STATUS;
> > +
> > +	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?