linux-kernel - Re: [RFC PATCH 1/1] platform-msi: Add platform check for subdevice irq domain

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Date:   Wed, 16 Dec 2020 09:42:54 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     David Woodhouse <dwmw2@...radead.org>, tglx@...utronix.de,
        ashok.raj@...el.com, kevin.tian@...el.com, dave.jiang@...el.com,
        megha.dey@...el.com
Cc:     baolu.lu@...ux.intel.com, alex.williamson@...hat.com,
        bhelgaas@...gle.com, dan.j.williams@...el.com,
        dmaengine@...r.kernel.org, eric.auger@...hat.com,
        jacob.jun.pan@...el.com, jgg@...lanox.com, jing.lin@...el.com,
        kvm@...r.kernel.org, kwankhede@...dia.com,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        maz@...nel.org, mona.hossain@...el.com, netanelg@...lanox.com,
        parav@...lanox.com, pbonzini@...hat.com, rafael@...nel.org,
        samuel.ortiz@...el.com, sanjay.k.kumar@...el.com,
        shahafs@...lanox.com, tony.luck@...el.com, vkoul@...nel.org,
        yan.y.zhao@...ux.intel.com, yi.l.liu@...el.com
Subject: Re: [RFC PATCH 1/1] platform-msi: Add platform check for subdevice
 irq domain

Hi David,

On 12/10/20 4:22 PM, David Woodhouse wrote:
> On Thu, 2020-12-10 at 08:46 +0800, Lu Baolu wrote:
>> +/*
>> + * We want to figure out which context we are running in. But the hardware
>> + * does not introduce a reliable way (instruction, CPUID leaf, MSR, whatever)
>> + * which can be manipulated by the VMM to let the OS figure out where it runs.
>> + * So we go with the below probably_on_bare_metal() function as a replacement
>> + * for definitely_on_bare_metal() to go forward only for the very simple reason
>> + * that this is the only option we have.
>> + */
>> +static const char * const possible_vmm_vendor_name[] = {
>> +       "QEMU", "Bochs", "KVM", "Xen", "VMware", "VMW", "VMware Inc.",
>> +       "innotek GmbH", "Oracle Corporation", "Parallels", "BHYVE",
>> +       "Microsoft Corporation"
>> +};
> 
> People do use SeaBIOS ("Bochs") on bare metal.

Is there any unique way to distinguish between running on bare metal and
VM?

> 
> You'll also see "Amazon EC2" on virt instances as well as bare metal
> instances. Although in that case I believe the virt instances do have
> the 'virtual machine' flag set in bit 4 of the BIOS Characteristics
> Extension Byte 2, and the bare metal obviously don't.
> 

So for Amazon EC2 case, we can use this byte to distinguish. Can you
please point me to the references of this Extension Byte (reference
code/spec or anything else) ?

Best regards,
baolu