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    SubjectRe: [PATCH v2 1/2] KVM: Start populating /sys/hypervisor with KVM entries
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    > On 14. May 2019, at 17:26, Christian Borntraeger <borntraeger@de.ibm.com> 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@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.

    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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