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Subject: Re: [PATCH v2 1/2] KVM: Start populating /sys/hypervisor with KVM
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To:     Filippo Sironi <sironi@amazon.de>, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org, boris.ostrovsky@oracle.com, cohuck@redhat.com,
        konrad.wilk@oracle.com, xen-devel@lists.xenproject.org,
        vasu.srinivasan@oracle.com
References: <1539078879-4372-1-git-send-email-sironi@amazon.de>
 <1557847002-23519-1-git-send-email-sironi@amazon.de>
 <1557847002-23519-2-git-send-email-sironi@amazon.de>
From:   Christian Borntraeger <borntraeger@de.ibm.com>
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Date:   Tue, 14 May 2019 17:26:36 +0200
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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@amazon.de>
> ---
> 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.


> +	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?

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