[PATCH v2 02/16] xen/riscv: implement arch_vcpu_{create,destroy}()

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

Introduce architecture-specific functions to create and destroy VCPUs.
Note that arch_vcpu_create() currently returns -EOPNOTSUPP, as the virtual
timer and interrupt controller are not yet implemented.

As part of this change, add continue_new_vcpu(), which will be used after
the first context_switch() of a new vCPU. Since this functionality is not
yet implemented, continue_new_vcpu() is currently provided as a stub.

Update the STACK_SIZE definition and introduce STACK_ORDER (to align with
other architectures) for allocating the vCPU stack.

Introduce struct cpu_info to store per-vCPU state that lives at the top
of the vCPU's stack.

Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
---
Changes in v2:
 - Drop BUILD_BUG_ON() in arch_vcpu_create() as a check isn't very useful.
 - Use vzalloc() instead of alloc_xenheap_page() to use the larger domheap to
   allocate vCPU's stack.
 - Drop printk() inside arch_vcpu_create() to not have potential big noise
   in console as it could be that an amount of vCPUs is pretty big.
 - Use XVFREE() instead of free_xenheap_pages() as vCPU's stack allocation
   happens with a usage of vzalloc() now.
 - Drop stack field as it is enough to have only cpu_info as stack pointer
   could be calculated based on cpu_info.
 - Drop cast when v.arch.cpu_info is inialized as it is not necessary
        to have it.
 - Drop memset() for arch.cpu_info() as it is enough to have vzalloc().
---
 xen/arch/riscv/Makefile              |  1 +
 xen/arch/riscv/domain.c              | 59 ++++++++++++++++++++++++++++
 xen/arch/riscv/include/asm/config.h  |  3 +-
 xen/arch/riscv/include/asm/current.h |  6 +++
 xen/arch/riscv/include/asm/domain.h  |  2 +
 xen/arch/riscv/stubs.c               | 10 -----
 6 files changed, 70 insertions(+), 11 deletions(-)
 create mode 100644 xen/arch/riscv/domain.c

diff --git a/xen/arch/riscv/Makefile b/xen/arch/riscv/Makefile
index 87c1148b0010..8863d4b15605 100644
--- a/xen/arch/riscv/Makefile
+++ b/xen/arch/riscv/Makefile
@@ -1,5 +1,6 @@
 obj-y += aplic.o
 obj-y += cpufeature.o
+obj-y += domain.o
 obj-$(CONFIG_EARLY_PRINTK) += early_printk.o
 obj-y += entry.o
 obj-y += imsic.o
diff --git a/xen/arch/riscv/domain.c b/xen/arch/riscv/domain.c
new file mode 100644
index 000000000000..9c546267881b
--- /dev/null
+++ b/xen/arch/riscv/domain.c
@@ -0,0 +1,59 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#include <xen/init.h>
+#include <xen/mm.h>
+#include <xen/sched.h>
+#include <xen/vmap.h>
+
+static void continue_new_vcpu(struct vcpu *prev)
+{
+    BUG_ON("unimplemented\n");
+}
+
+static void __init __maybe_unused build_assertions(void)
+{
+    /*
+     * Enforce the requirement documented in struct cpu_info that
+     * guest_cpu_user_regs must be the first field.
+     */
+    BUILD_BUG_ON(offsetof(struct cpu_info, guest_cpu_user_regs) != 0);
+}
+
+int arch_vcpu_create(struct vcpu *v)
+{
+    int rc = 0;
+    void *stack = vzalloc(STACK_SIZE);
+
+    if ( !stack )
+        return -ENOMEM;
+
+    v->arch.cpu_info = stack + STACK_SIZE - sizeof(struct cpu_info);
+    memset(v->arch.cpu_info, 0, sizeof(*v->arch.cpu_info));
+
+    v->arch.xen_saved_context.sp = (register_t)v->arch.cpu_info;
+    v->arch.xen_saved_context.ra = (register_t)continue_new_vcpu;
+
+    /* Idle VCPUs don't need the rest of this setup */
+    if ( is_idle_vcpu(v) )
+        return rc;
+
+    /*
+     * As the vtimer and interrupt controller (IC) are not yet implemented,
+     * return an error.
+     *
+     * TODO: Drop this once the vtimer and IC are implemented.
+     */
+    rc = -EOPNOTSUPP;
+    goto fail;
+
+    return rc;
+
+ fail:
+    arch_vcpu_destroy(v);
+    return rc;
+}
+
+void arch_vcpu_destroy(struct vcpu *v)
+{
+    vfree((char *)v->arch.cpu_info + sizeof(struct cpu_info));
+}
diff --git a/xen/arch/riscv/include/asm/config.h 
b/xen/arch/riscv/include/asm/config.h
index 1e08d3bf78be..86a95df018b5 100644
--- a/xen/arch/riscv/include/asm/config.h
+++ b/xen/arch/riscv/include/asm/config.h
@@ -143,7 +143,8 @@
 
 #define SMP_CACHE_BYTES (1 << 6)
 
-#define STACK_SIZE PAGE_SIZE
+#define STACK_ORDER 3
+#define STACK_SIZE (PAGE_SIZE << STACK_ORDER)
 
 #define IDENT_AREA_SIZE 64
 
diff --git a/xen/arch/riscv/include/asm/current.h 
b/xen/arch/riscv/include/asm/current.h
index 0c3ea70c2ec8..58c9f1506b7c 100644
--- a/xen/arch/riscv/include/asm/current.h
+++ b/xen/arch/riscv/include/asm/current.h
@@ -21,6 +21,12 @@ struct pcpu_info {
 /* tp points to one of these */
 extern struct pcpu_info pcpu_info[NR_CPUS];
 
+/* Per-VCPU state that lives at the top of the stack */
+struct cpu_info {
+    /* This should be the first member. */
+    struct cpu_user_regs guest_cpu_user_regs;
+};
+
 #define set_processor_id(id)    do { \
     tp->processor_id = (id);         \
 } while (0)
diff --git a/xen/arch/riscv/include/asm/domain.h 
b/xen/arch/riscv/include/asm/domain.h
index 0d9b4c4b525e..ec7786c76199 100644
--- a/xen/arch/riscv/include/asm/domain.h
+++ b/xen/arch/riscv/include/asm/domain.h
@@ -49,6 +49,8 @@ struct arch_vcpu
         register_t ra;
     } xen_saved_context;
 
+    struct cpu_info *cpu_info;
+
     /* CSRs */
     register_t hedeleg;
     register_t hideleg;
diff --git a/xen/arch/riscv/stubs.c b/xen/arch/riscv/stubs.c
index 29bdb65afbdf..9e30a9a3b50b 100644
--- a/xen/arch/riscv/stubs.c
+++ b/xen/arch/riscv/stubs.c
@@ -121,16 +121,6 @@ void dump_pageframe_info(struct domain *d)
     BUG_ON("unimplemented");
 }
 
-int arch_vcpu_create(struct vcpu *v)
-{
-    BUG_ON("unimplemented");
-}
-
-void arch_vcpu_destroy(struct vcpu *v)
-{
-    BUG_ON("unimplemented");
-}
-
 void vcpu_switch_to_aarch64_mode(struct vcpu *v)
 {
     BUG_ON("unimplemented");
-- 
2.52.0