Add a RISC-V implementation of vcpu_kick(), which unblocks the target
vCPU and sends an event check IPI if the vCPU was running on another
processor. This mirrors the behavior of Arm and enables proper vCPU
wakeup handling on RISC-V.

Remove the stub implementation from stubs.c, as it is now provided by
arch/riscv/domain.c.

Since vcpu_kick() calls perfc_incr(vcpu_kick), add perfcounter for
vcpu_kick to handle the case when CONFIG_PERF_COUNTERS=y. Although
CONFIG_PERF_COUNTERS is not enabled by default, it can be enabled,
for example, by randconfig what will lead to CI build issues.

Signed-off-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
---
Changes in v4-v5:
 - Nothing changed. Only rebase.
---
Changes in v3:
 - Add asm/perfc_defn.h to provide vcpu_kick perfcoounter to cover
   the case when CONFIG_PERF_COUNTERS=y.
---
Changes in v2:
 - Add Acked-by: Jan Beulich <jbeulich@suse.com>.
---
 xen/arch/riscv/domain.c                 | 14 ++++++++++++++
 xen/arch/riscv/include/asm/Makefile     |  1 -
 xen/arch/riscv/include/asm/perfc_defn.h |  3 +++
 xen/arch/riscv/stubs.c                  |  5 -----
 4 files changed, 17 insertions(+), 6 deletions(-)
 create mode 100644 xen/arch/riscv/include/asm/perfc_defn.h

diff --git a/xen/arch/riscv/domain.c b/xen/arch/riscv/domain.c
index 7027b5e9aa20..fb5c21078172 100644
--- a/xen/arch/riscv/domain.c
+++ b/xen/arch/riscv/domain.c
@@ -1,9 +1,11 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
 
+#include <xen/cpumask.h>
 #include <xen/init.h>
 #include <xen/mm.h>
 #include <xen/sections.h>
 #include <xen/sched.h>
+#include <xen/smp.h>
 #include <xen/vmap.h>
 
 #include <asm/bitops.h>
@@ -251,6 +253,18 @@ void vcpu_flush_interrupts(struct vcpu *v)
 #endif
 }
 
+void vcpu_kick(struct vcpu *v)
+{
+    bool running = v->is_running;
+
+    vcpu_unblock(v);
+    if ( running && v != current )
+    {
+        perfc_incr(vcpu_kick);
+        smp_send_event_check_mask(cpumask_of(v->processor));
+    }
+}
+
 static void __init __maybe_unused build_assertions(void)
 {
     /*
diff --git a/xen/arch/riscv/include/asm/Makefile b/xen/arch/riscv/include/asm/Makefile
index 3824f31c395c..86c56251d5d7 100644
--- a/xen/arch/riscv/include/asm/Makefile
+++ b/xen/arch/riscv/include/asm/Makefile
@@ -7,7 +7,6 @@ generic-y += hypercall.h
 generic-y += iocap.h
 generic-y += irq-dt.h
 generic-y += percpu.h
-generic-y += perfc_defn.h
 generic-y += random.h
 generic-y += softirq.h
 generic-y += vm_event.h
diff --git a/xen/arch/riscv/include/asm/perfc_defn.h b/xen/arch/riscv/include/asm/perfc_defn.h
new file mode 100644
index 000000000000..8a4b945df662
--- /dev/null
+++ b/xen/arch/riscv/include/asm/perfc_defn.h
@@ -0,0 +1,3 @@
+/* This file is intended to be included multiple times. */
+
+PERFCOUNTER(vcpu_kick, "vcpu: notify other vcpu")
diff --git a/xen/arch/riscv/stubs.c b/xen/arch/riscv/stubs.c
index daadff0138e4..eedf8bf9350a 100644
--- a/xen/arch/riscv/stubs.c
+++ b/xen/arch/riscv/stubs.c
@@ -203,11 +203,6 @@ void vcpu_block_unless_event_pending(struct vcpu *v)
     BUG_ON("unimplemented");
 }
 
-void vcpu_kick(struct vcpu *v)
-{
-    BUG_ON("unimplemented");
-}
-
 unsigned long
 hypercall_create_continuation(unsigned int op, const char *format, ...)
 {
-- 
2.53.0