[PATCH v2 2/2] xen: add sysfs node for guest type

[Juergen Gross <jgross@suse.com>]

Currently there is no reliable user interface inside a Xen guest to
determine its type (e.g. HVM, PV or PVH). Instead of letting user mode
try to determine this by various rather hacky mechanisms (parsing of
boot messages before they are gone, trying to make use of known subtle
differences in behavior of some instructions), add a sysfs node
/sys/hypervisor/guest_type to explicitly deliver this information as
it is known to the kernel.

Signed-off-by: Juergen Gross <jgross@suse.com>
---
V2:
  - remove PVHVM guest type (Andrew Cooper)
  - move description to Documentation/ABI/testing/sysfs-hypervisor-xen
    (Boris Ostrovsky)
  - make xen_guest_type const char * (Jan Beulich)
  - modify standard ARM guest type to "Xen"
---
 .../{sysfs-hypervisor-pmu => sysfs-hypervisor-xen}      | 15 +++++++++++++--
 MAINTAINERS                                             |  2 +-
 arch/arm/xen/enlighten.c                                |  3 +++
 arch/x86/xen/enlighten.c                                |  3 +++
 arch/x86/xen/enlighten_hvm.c                            |  5 +++--
 arch/x86/xen/enlighten_pv.c                             |  1 +
 drivers/xen/sys-hypervisor.c                            | 17 +++++++++++++++++
 include/xen/xen.h                                       |  2 ++
 8 files changed, 43 insertions(+), 5 deletions(-)
 rename Documentation/ABI/testing/{sysfs-hypervisor-pmu => sysfs-hypervisor-xen} (67%)

diff --git a/Documentation/ABI/testing/sysfs-hypervisor-pmu b/Documentation/ABI/testing/sysfs-hypervisor-xen
similarity index 67%
rename from Documentation/ABI/testing/sysfs-hypervisor-pmu
rename to Documentation/ABI/testing/sysfs-hypervisor-xen
index 224faa105e18..c0edb3fdd6eb 100644
--- a/Documentation/ABI/testing/sysfs-hypervisor-pmu
+++ b/Documentation/ABI/testing/sysfs-hypervisor-xen
@@ -1,8 +1,19 @@
+What:		/sys/hypervisor/guest_type
+Date:		May 2017
+KernelVersion:	4.13
+Contact:	xen-devel@lists.xenproject.org
+Description:	If running under Xen:
+		Type of guest:
+		"Xen": standard guest type on arm
+		"HVM": fully virtualized guest (x86)
+		"PV": paravirtualized guest (x86)
+		"PVH": fully virtualized guest without legacy emulation (x86)
+
 What:		/sys/hypervisor/pmu/pmu_mode
 Date:		August 2015
 KernelVersion:	4.3
 Contact:	Boris Ostrovsky <boris.ostrovsky@oracle.com>
-Description:
+Description:	If running under Xen:
 		Describes mode that Xen's performance-monitoring unit (PMU)
 		uses. Accepted values are
 			"off"  -- PMU is disabled
@@ -17,7 +28,7 @@ What:           /sys/hypervisor/pmu/pmu_features
 Date:           August 2015
 KernelVersion:  4.3
 Contact:        Boris Ostrovsky <boris.ostrovsky@oracle.com>
-Description:
+Description:	If running under Xen:
 		Describes Xen PMU features (as an integer). A set bit indicates
 		that the corresponding feature is enabled. See
 		include/xen/interface/xenpmu.h for available features
diff --git a/MAINTAINERS b/MAINTAINERS
index 5d10cc33fc41..76a0fecfca51 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -13984,7 +13984,7 @@ F:	arch/x86/include/asm/xen/
 F:	include/xen/
 F:	include/uapi/xen/
 F:	Documentation/ABI/stable/sysfs-hypervisor-xen
-F:	Documentation/ABI/testing/sysfs-hypervisor-pmu
+F:	Documentation/ABI/testing/sysfs-hypervisor-xen
 
 XEN HYPERVISOR ARM
 M:	Stefano Stabellini <sstabellini@kernel.org>
diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
index ba7f4c8f5c3e..7429af623379 100644
--- a/arch/arm/xen/enlighten.c
+++ b/arch/arm/xen/enlighten.c
@@ -43,6 +43,9 @@ EXPORT_SYMBOL(xen_start_info);
 enum xen_domain_type xen_domain_type = XEN_NATIVE;
 EXPORT_SYMBOL(xen_domain_type);
 
+const char *xen_guest_type = "Xen";
+EXPORT_SYMBOL_GPL(xen_guest_type);
+
 struct shared_info xen_dummy_shared_info;
 struct shared_info *HYPERVISOR_shared_info = (void *)&xen_dummy_shared_info;
 
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index a5ffcbb20cc0..17b6503df291 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -47,6 +47,9 @@ EXPORT_PER_CPU_SYMBOL(xen_vcpu_id);
 enum xen_domain_type xen_domain_type = XEN_NATIVE;
 EXPORT_SYMBOL_GPL(xen_domain_type);
 
+const char *xen_guest_type = "HVM";
+EXPORT_SYMBOL_GPL(xen_guest_type);
+
 unsigned long *machine_to_phys_mapping = (void *)MACH2PHYS_VIRT_START;
 EXPORT_SYMBOL(machine_to_phys_mapping);
 unsigned long  machine_to_phys_nr;
diff --git a/arch/x86/xen/enlighten_hvm.c b/arch/x86/xen/enlighten_hvm.c
index a6d014f47e52..bda98726d139 100644
--- a/arch/x86/xen/enlighten_hvm.c
+++ b/arch/x86/xen/enlighten_hvm.c
@@ -68,9 +68,10 @@ static void __init init_hvm_pv_info(void)
 	xen_domain_type = XEN_HVM_DOMAIN;
 
 	/* PVH set up hypercall page in xen_prepare_pvh(). */
-	if (xen_pvh_domain())
+	if (xen_pvh_domain()) {
 		pv_info.name = "Xen PVH";
-	else {
+		xen_guest_type = "PVH";
+	} else {
 		u64 pfn;
 		uint32_t msr;
 
diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
index f33eef4ebd12..7ac5e93d96f3 100644
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -1255,6 +1255,7 @@ asmlinkage __visible void __init xen_start_kernel(void)
 		return;
 
 	xen_domain_type = XEN_PV_DOMAIN;
+	xen_guest_type = "PV";
 
 	xen_setup_features();
 
diff --git a/drivers/xen/sys-hypervisor.c b/drivers/xen/sys-hypervisor.c
index 84106f9c456c..d641e9970d5d 100644
--- a/drivers/xen/sys-hypervisor.c
+++ b/drivers/xen/sys-hypervisor.c
@@ -50,6 +50,18 @@ static int __init xen_sysfs_type_init(void)
 	return sysfs_create_file(hypervisor_kobj, &type_attr.attr);
 }
 
+static ssize_t guest_type_show(struct hyp_sysfs_attr *attr, char *buffer)
+{
+	return sprintf(buffer, "%s\n", xen_guest_type);
+}
+
+HYPERVISOR_ATTR_RO(guest_type);
+
+static int __init xen_sysfs_guest_type_init(void)
+{
+	return sysfs_create_file(hypervisor_kobj, &guest_type_attr.attr);
+}
+
 /* xen version attributes */
 static ssize_t major_show(struct hyp_sysfs_attr *attr, char *buffer)
 {
@@ -471,6 +483,9 @@ static int __init hyper_sysfs_init(void)
 	ret = xen_sysfs_type_init();
 	if (ret)
 		goto out;
+	ret = xen_sysfs_guest_type_init();
+	if (ret)
+		goto guest_type_out;
 	ret = xen_sysfs_version_init();
 	if (ret)
 		goto version_out;
@@ -502,6 +517,8 @@ static int __init hyper_sysfs_init(void)
 comp_out:
 	sysfs_remove_group(hypervisor_kobj, &version_group);
 version_out:
+	sysfs_remove_file(hypervisor_kobj, &guest_type_attr.attr);
+guest_type_out:
 	sysfs_remove_file(hypervisor_kobj, &type_attr.attr);
 out:
 	return ret;
diff --git a/include/xen/xen.h b/include/xen/xen.h
index 6e8b7fc79801..f02d1732d7a6 100644
--- a/include/xen/xen.h
+++ b/include/xen/xen.h
@@ -9,8 +9,10 @@ enum xen_domain_type {
 
 #ifdef CONFIG_XEN
 extern enum xen_domain_type xen_domain_type;
+extern const char *xen_guest_type;
 #else
 #define xen_domain_type		XEN_NATIVE
+#define xen_guest_type		"native"
 #endif
 
 #define xen_domain()		(xen_domain_type != XEN_NATIVE)
-- 
2.12.0