[RFC PATCH 01/16] x86/xen: add xenhost_t interface

[Ankur Arora]

Add xenhost_t which will serve as an abstraction over Xen interfaces.
It co-exists with the PV/HVM/PVH abstractions (x86_init, hypervisor_x86,
pv_ops etc) and is meant to capture mechanisms for communication with
Xen so we could have different types of underlying Xen: regular, local,
and nested.

Also add xenhost_register() and stub registration in the various guest
types.

Signed-off-by: Ankur Arora <ankur.a.arora@xxxxxxxxxx>
---
 arch/x86/xen/Makefile        |  1 +
 arch/x86/xen/enlighten_hvm.c | 13 +++++
 arch/x86/xen/enlighten_pv.c  | 16 ++++++
 arch/x86/xen/enlighten_pvh.c | 12 +++++
 arch/x86/xen/xenhost.c       | 75 ++++++++++++++++++++++++++++
 include/xen/xen.h            |  3 ++
 include/xen/xenhost.h        | 95 ++++++++++++++++++++++++++++++++++++
 7 files changed, 215 insertions(+)
 create mode 100644 arch/x86/xen/xenhost.c
 create mode 100644 include/xen/xenhost.h

diff --git a/arch/x86/xen/Makefile b/arch/x86/xen/Makefile
index 084de77a109e..564b4dddbc15 100644
--- a/arch/x86/xen/Makefile
+++ b/arch/x86/xen/Makefile
@@ -18,6 +18,7 @@ obj-y				+= mmu.o
 obj-y				+= time.o
 obj-y				+= grant-table.o
 obj-y				+= suspend.o
+obj-y				+= xenhost.o
 
 obj-$(CONFIG_XEN_PVHVM)		+= enlighten_hvm.o
 obj-$(CONFIG_XEN_PVHVM)		+= mmu_hvm.o
diff --git a/arch/x86/xen/enlighten_hvm.c b/arch/x86/xen/enlighten_hvm.c
index 0e75642d42a3..100452f4f44c 100644
--- a/arch/x86/xen/enlighten_hvm.c
+++ b/arch/x86/xen/enlighten_hvm.c
@@ -5,6 +5,7 @@
 #include <linux/kexec.h>
 #include <linux/memblock.h>
 
+#include <xen/xenhost.h>
 #include <xen/features.h>
 #include <xen/events.h>
 #include <xen/interface/memory.h>
@@ -82,6 +83,12 @@ static void __init xen_hvm_init_mem_mapping(void)
 	xen_vcpu_info_reset(0);
 }
 
+xenhost_ops_t xh_hvm_ops = {
+};
+
+xenhost_ops_t xh_hvm_nested_ops = {
+};
+
 static void __init init_hvm_pv_info(void)
 {
 	int major, minor;
@@ -179,6 +186,12 @@ static void __init xen_hvm_guest_init(void)
 {
 	if (xen_pv_domain())
 		return;
+	/*
+	 * We need only xenhost_r1 for HVM guests since they cannot be
+	 * driver domain (?) or dom0.
+	 */
+	if (!xen_pvh_domain())
+		xenhost_register(xenhost_r1, &xh_hvm_ops);
 
 	init_hvm_pv_info();
 
diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
index c54a493e139a..bb6e811c1525 100644
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -36,6 +36,7 @@
 
 #include <xen/xen.h>
 #include <xen/events.h>
+#include <xen/xenhost.h>
 #include <xen/interface/xen.h>
 #include <xen/interface/version.h>
 #include <xen/interface/physdev.h>
@@ -1188,6 +1189,12 @@ static void __init xen_dom0_set_legacy_features(void)
 	x86_platform.legacy.rtc = 1;
 }
 
+xenhost_ops_t xh_pv_ops = {
+};
+
+xenhost_ops_t xh_pv_nested_ops = {
+};
+
 /* First C function to be called on Xen boot */
 asmlinkage __visible void __init xen_start_kernel(void)
 {
@@ -1198,6 +1205,15 @@ asmlinkage __visible void __init xen_start_kernel(void)
 	if (!xen_start_info)
 		return;
 
+	xenhost_register(xenhost_r1, &xh_pv_ops);
+
+	/*
+	 * Detect in some implementation defined manner whether this is
+	 * nested or not.
+	 */
+	if (xen_driver_domain() && xen_nested())
+		xenhost_register(xenhost_r2, &xh_pv_nested_ops);
+
 	xen_domain_type = XEN_PV_DOMAIN;
 	xen_start_flags = xen_start_info->flags;
 
diff --git a/arch/x86/xen/enlighten_pvh.c b/arch/x86/xen/enlighten_pvh.c
index 35b7599d2d0b..826c296d27a3 100644
--- a/arch/x86/xen/enlighten_pvh.c
+++ b/arch/x86/xen/enlighten_pvh.c
@@ -8,6 +8,7 @@
 #include <asm/e820/api.h>
 
 #include <xen/xen.h>
+#include <xen/xenhost.h>
 #include <asm/xen/interface.h>
 #include <asm/xen/hypercall.h>
 
@@ -21,11 +22,22 @@
  */
 bool xen_pvh __attribute__((section(".data"))) = 0;
 
+extern xenhost_ops_t xh_hvm_ops, xh_hvm_nested_ops;
+
 void __init xen_pvh_init(void)
 {
 	u32 msr;
 	u64 pfn;
 
+	xenhost_register(xenhost_r1, &xh_hvm_ops);
+
+	/*
+	 * Detect in some implementation defined manner whether this is
+	 * nested or not.
+	 */
+	if (xen_driver_domain() && xen_nested())
+		xenhost_register(xenhost_r2, &xh_hvm_nested_ops);
+
 	xen_pvh = 1;
 	xen_start_flags = pvh_start_info.flags;
 
diff --git a/arch/x86/xen/xenhost.c b/arch/x86/xen/xenhost.c
new file mode 100644
index 000000000000..ca90acd7687e
--- /dev/null
+++ b/arch/x86/xen/xenhost.c
@@ -0,0 +1,75 @@
+#include <linux/types.h>
+#include <linux/bug.h>
+#include <xen/xen.h>
+#include <xen/xenhost.h>
+
+xenhost_t xenhosts[2];
+/*
+ * xh_default: interface to the regular hypervisor. xenhost_type is xenhost_r0
+ * or xenhost_r1.
+ *
+ * xh_remote: interface to remote hypervisor. Needed for PV driver support on
+ * L1-dom0/driver-domain for nested Xen. xenhost_type is xenhost_r2.
+ */
+xenhost_t *xh_default = (xenhost_t *) &xenhosts[0];
+xenhost_t *xh_remote = (xenhost_t *) &xenhosts[1];
+
+/*
+ * Exported for use of for_each_xenhost().
+ */
+EXPORT_SYMBOL_GPL(xenhosts);
+
+/*
+ * Some places refer directly to a specific type of xenhost.
+ * This might be better as a macro though.
+ */
+EXPORT_SYMBOL_GPL(xh_default);
+EXPORT_SYMBOL_GPL(xh_remote);
+
+void xenhost_register(enum xenhost_type type, xenhost_ops_t *ops)
+{
+	switch (type) {
+		case xenhost_r0:
+		case xenhost_r1:
+			BUG_ON(xh_default->type != xenhost_invalid);
+
+			xh_default->type = type;
+			xh_default->ops = ops;
+			break;
+		case xenhost_r2:
+			BUG_ON(xh_remote->type != xenhost_invalid);
+
+			/*
+			 * We should have a default xenhost by the
+			 * time xh_remote is registered.
+			 */
+			BUG_ON(!xh_default);
+
+			xh_remote->type = type;
+			xh_remote->ops = ops;
+			break;
+		default:
+			BUG();
+	}
+}
+
+/*
+ * __xenhost_unregister: expected to be called only if there's an
+ * error early in the init.
+ */
+void __xenhost_unregister(enum xenhost_type type)
+{
+	switch (type) {
+		case xenhost_r0:
+		case xenhost_r1:
+			xh_default->type = xenhost_invalid;
+			xh_default->ops = NULL;
+			break;
+		case xenhost_r2:
+			xh_remote->type = xenhost_invalid;
+			xh_remote->ops = NULL;
+			break;
+		default:
+			BUG();
+	}
+}
diff --git a/include/xen/xen.h b/include/xen/xen.h
index 0e2156786ad2..540db8459536 100644
--- a/include/xen/xen.h
+++ b/include/xen/xen.h
@@ -42,6 +42,9 @@ extern struct hvm_start_info pvh_start_info;
 #define xen_initial_domain()	(0)
 #endif	/* CONFIG_XEN_DOM0 */
 
+#define xen_driver_domain()	xen_initial_domain()
+#define xen_nested()	0
+
 struct bio_vec;
 bool xen_biovec_phys_mergeable(const struct bio_vec *vec1,
 		const struct bio_vec *vec2);
diff --git a/include/xen/xenhost.h b/include/xen/xenhost.h
new file mode 100644
index 000000000000..a58e883f144e
--- /dev/null
+++ b/include/xen/xenhost.h
@@ -0,0 +1,95 @@
+#ifndef __XENHOST_H
+#define __XENHOST_H
+
+/*
+ * Xenhost abstracts out the Xen interface. It co-exists with the PV/HVM/PVH
+ * abstractions (x86_init, hypervisor_x86, pv_ops etc) and is meant to
+ * expose ops for communication between the guest and Xen (hypercall, cpuid,
+ * shared_info/vcpu_info, evtchn, grant-table and on top of those, xenbus, ballooning),
+ * so these could differ based on the kind of underlying Xen: regular, local,
+ * and nested.
+ *
+ * Any call-sites which initiate communication with the hypervisor take
+ * xenhost_t * as a parameter and use the appropriate xenhost interface.
+ *
+ * Note, that the init for the nested xenhost (in the nested dom0 case,
+ * there are two) happens for each operation alongside the default xenhost
+ * (which remains similar to the one now) and is not deferred for later.
+ * This allows us to piggy-back on the non-trivial sequencing, inter-locking
+ * logic in the init of the default xenhost.
+ */
+
+/*
+ * xenhost_type: specifies the controlling Xen interface. The notation,
+ * xenhost_r0, xenhost_r1, xenhost_r2 is meant to invoke hypervisor distance
+ * from the guest.
+ *
+ * Note that the distance is relative, and so does not identify a specific
+ * hypervisor, just the role played by the interface: so, instance for L0-guest
+ * xenhost_r1 would be L0-Xen and for an L1-guest, L1-Xen.
+ */
+enum xenhost_type {
+	xenhost_invalid = 0,
+	/*
+	 * xenhost_r1: the guest's frontend or backend drivers talking
+	 * to a hypervisor one level removed.
+	 * This is the ordinary, non-nested configuration as well as for the
+	 * typical nested frontends and backends.
+	 *
+	 * The corresponding xenhost_t would continue to use the current
+	 * interfaces, via a redirection layer.
+	 */
+	xenhost_r1,
+
+	/*
+	 * xenhost_r2: frontend drivers communicating with a hypervisor two
+	 * levels removed: so L1-dom0-frontends communicating with L0-Xen.
+	 *
+	 * This is the nested-Xen configuration: L1-dom0-frontend drivers can
+	 * now talk to L0-dom0-backend drivers via a separate xenhost_t.
+	 */
+	xenhost_r2,
+
+	/*
+	 * Local/Co-located case: backend drivers now run in the same address
+	 * space as the hypervisor. The driver model remains same as
+	 * xenhost_r1, but with slightly different interfaces.
+	 *
+	 * Any frontend guests of this hypervisor will continue to be
+	 * xenhost_r1.
+	 */
+	xenhost_r0,
+};
+
+struct xenhost_ops;
+
+typedef struct {
+	enum xenhost_type type;
+
+	struct xenhost_ops *ops;
+} xenhost_t;
+
+typedef struct xenhost_ops {
+} xenhost_ops_t;
+
+extern xenhost_t *xh_default, *xh_remote;
+extern xenhost_t xenhosts[2];
+
+/*
+ * xenhost_register(): is called early in the guest's xen-init, after it detects
+ * in some implementation defined manner what kind of underlying xenhost or
+ * xenhosts exist.
+ * Specifies the type of xenhost being registered and the ops for that.
+ */
+void xenhost_register(enum xenhost_type type, xenhost_ops_t *ops);
+void __xenhost_unregister(enum xenhost_type type);
+
+
+/*
+ * Convoluted interface so we can do this without adding a loop counter.
+ */
+#define for_each_xenhost(xh) \
+	for ((xh) = (xenhost_t **) &xenhosts[0];	\
+		(((xh) - (xenhost_t **)&xenhosts) < 2) && (*xh)->type != xenhost_invalid; (xh)++)
+
+#endif /* __XENHOST_H */
-- 
2.20.1