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

Sironi, Filippo
2019-05-17T15:41:50Z

> On 16. May 2019, at 15:50, Graf, Alexander <graf@amazon.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@amazon.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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