linux-kernel - Re: [PATCH v2 1/2] KVM: Start populating /sys/hypervisor with KVM entries

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Message-ID: <3D2C4EE3-1C2E-4032-9964-31A066E542AA@amazon.de>
Date:   Fri, 17 May 2019 15:41:39 +0000
From:   "Sironi, Filippo" <sironi@...zon.de>
To:     "Graf, Alexander" <graf@...zon.com>
CC:     LKML <linux-kernel@...r.kernel.org>,
        KVM list <kvm@...r.kernel.org>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        "cohuck@...hat.com" <cohuck@...hat.com>,
        "konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>
Subject: Re: [PATCH v2 1/2] KVM: Start populating /sys/hypervisor with KVM
 entries


> On 16. May 2019, at 15:50, Graf, Alexander <graf@...zon.com> wrote:
> 
> On 14.05.19 08:16, Filippo Sironi wrote:
>> Start populating /sys/hypervisor with KVM entries when we're running on
>> KVM. This is to replicate functionality that's available when we're
>> running on Xen.
>> 
>> Start with /sys/hypervisor/uuid, which users prefer over
>> /sys/devices/virtual/dmi/id/product_uuid as a way to recognize a virtual
>> machine, since it's also available when running on Xen HVM and on Xen PV
>> and, on top of that doesn't require root privileges by default.
>> Let's create arch-specific hooks so that different architectures can
>> provide different implementations.
>> 
>> Signed-off-by: Filippo Sironi <sironi@...zon.de>
> 
> I think this needs something akin to
> 
>  https://www.kernel.org/doc/Documentation/ABI/stable/sysfs-hypervisor-xen
> 
> to document which files are available.
> 
>> ---
>> v2:
>> * move the retrieval of the VM UUID out of uuid_show and into
>>  kvm_para_get_uuid, which is a weak function that can be overwritten
>> 
>> drivers/Kconfig              |  2 ++
>> drivers/Makefile             |  2 ++
>> drivers/kvm/Kconfig          | 14 ++++++++++++++
>> drivers/kvm/Makefile         |  1 +
>> drivers/kvm/sys-hypervisor.c | 30 ++++++++++++++++++++++++++++++
>> 5 files changed, 49 insertions(+)
>> create mode 100644 drivers/kvm/Kconfig
>> create mode 100644 drivers/kvm/Makefile
>> create mode 100644 drivers/kvm/sys-hypervisor.c
>> 
> 
> [...]
> 
>> +
>> +__weak const char *kvm_para_get_uuid(void)
>> +{
>> +	return NULL;
>> +}
>> +
>> +static ssize_t uuid_show(struct kobject *obj,
>> +			 struct kobj_attribute *attr,
>> +			 char *buf)
>> +{
>> +	const char *uuid = kvm_para_get_uuid();
>> +	return sprintf(buf, "%s\n", uuid);
> 
> The usual return value for the Xen /sys/hypervisor interface is
> "<denied>". Wouldn't it make sense to follow that pattern for the KVM
> one too? Currently, if we can not determine the UUID this will just
> return (null).
> 
> Otherwise, looks good to me. Are you aware of any other files we should
> provide? Also, is there any reason not to implement ARM as well while at it?
> 
> Alex

This originated from a customer request that was using /sys/hypervisor/uuid.
My guess is that we would want to expose "type" and "version" moving
forward and that's when we hypervisor hooks will be useful on top
of arch hooks.

On a different note, any idea how to check whether the OS is running
virtualized on KVM on ARM and ARM64?  kvm_para_available() isn't an
option and the same is true for S390 where kvm_para_available()
always returns true and it would even if a KVM enabled kernel would
be running on bare metal.

I think we will need another arch hook to call a function that says
whether the OS is running virtualized on KVM.

>> +}
>> +
>> +static struct kobj_attribute uuid = __ATTR_RO(uuid);
>> +
>> +static int __init uuid_init(void)
>> +{
>> +	if (!kvm_para_available())
>> +		return 0;
>> +	return sysfs_create_file(hypervisor_kobj, &uuid.attr);
>> +}
>> +
>> +device_initcall(uuid_init);




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