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

[Sironi, Filippo]

> On 14. May 2019, at 17:26, Christian Borntraeger <borntraeger@xxxxxxxxxx> wrote:
> 
> 
> 
> On 14.05.19 17:16, 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@xxxxxxxxx>
>> ---
>> 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
>> 
>> diff --git a/drivers/Kconfig b/drivers/Kconfig
>> index 45f9decb9848..90eb835fe951 100644
>> --- a/drivers/Kconfig
>> +++ b/drivers/Kconfig
>> @@ -146,6 +146,8 @@ source "drivers/hv/Kconfig"
>> 
>> source "drivers/xen/Kconfig"
>> 
>> +source "drivers/kvm/Kconfig"
>> +
>> source "drivers/staging/Kconfig"
>> 
>> source "drivers/platform/Kconfig"
>> diff --git a/drivers/Makefile b/drivers/Makefile
>> index c61cde554340..79cc92a3f6bf 100644
>> --- a/drivers/Makefile
>> +++ b/drivers/Makefile
>> @@ -44,6 +44,8 @@ obj-y				+= soc/
>> obj-$(CONFIG_VIRTIO)		+= virtio/
>> obj-$(CONFIG_XEN)		+= xen/
>> 
>> +obj-$(CONFIG_KVM_GUEST)		+= kvm/
>> +
>> # regulators early, since some subsystems rely on them to initialize
>> obj-$(CONFIG_REGULATOR)		+= regulator/
>> 
>> diff --git a/drivers/kvm/Kconfig b/drivers/kvm/Kconfig
>> new file mode 100644
>> index 000000000000..3fc041df7c11
>> --- /dev/null
>> +++ b/drivers/kvm/Kconfig
>> @@ -0,0 +1,14 @@
>> +menu "KVM driver support"
>> +        depends on KVM_GUEST
>> +
>> +config KVM_SYS_HYPERVISOR
>> +        bool "Create KVM entries under /sys/hypervisor"
>> +        depends on SYSFS
>> +        select SYS_HYPERVISOR
>> +        default y
>> +        help
>> +          Create KVM entries under /sys/hypervisor (e.g., uuid). When running
>> +          native or on another hypervisor, /sys/hypervisor may still be
>> +          present, but it will have no KVM entries.
>> +
>> +endmenu
>> diff --git a/drivers/kvm/Makefile b/drivers/kvm/Makefile
>> new file mode 100644
>> index 000000000000..73a43fc994b9
>> --- /dev/null
>> +++ b/drivers/kvm/Makefile
>> @@ -0,0 +1 @@
>> +obj-$(CONFIG_KVM_SYS_HYPERVISOR) += sys-hypervisor.o
>> diff --git a/drivers/kvm/sys-hypervisor.c b/drivers/kvm/sys-hypervisor.c
>> new file mode 100644
>> index 000000000000..43b1d1a09807
>> --- /dev/null
>> +++ b/drivers/kvm/sys-hypervisor.c
>> @@ -0,0 +1,30 @@
>> +/* SPDX-License-Identifier: GPL-2.0 */
>> +
>> +#include <asm/kvm_para.h>
>> +
>> +#include <linux/kobject.h>
>> +#include <linux/sysfs.h>
>> +
>> +__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();
> 
> I would prefer to have kvm_para_get_uuid return a uuid_t
> but char * will probably work out as well.

Let me give this a quick spin.

>> +	return sprintf(buf, "%s\n", uuid);
>> +}
>> +
>> +static struct kobj_attribute uuid = __ATTR_RO(uuid);
>> +
>> +static int __init uuid_init(void)
>> +{
>> +	if (!kvm_para_available())
> 
> Isnt kvm_para_available a function that is defined in the context of the HOST
> and not of the guest?

No, kvm_para_available is defined in the guest context.
On x86, it checks for the presence of the KVM CPUID leafs.

>> +		return 0;
>> +	return sysfs_create_file(hypervisor_kobj, &uuid.attr);
>> +}
>> +
>> +device_initcall(uuid_init);




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