[xen staging] xen/riscv: implement arch_vcpu_{create,destroy}()

[patchbot@xxxxxxx]

commit ad535118f0f1e5cb4b1dfb2580efcfe728717194
Author:     Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
AuthorDate: Wed Feb 18 10:16:34 2026 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Wed Feb 18 10:16:34 2026 +0100

    xen/riscv: implement arch_vcpu_{create,destroy}()
    
    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.
    
    Add callee-saved registers to struct arch_vcpu which are  used to preserve
    Xenâ??s own execution context when switching between vCPU stacks.
    It is going to be used in the following way (pseudocode):
      context_switch(prev_vcpu, next_vcpu):
        ...
    
        /* Switch from previous stack to the next stack. */
        __context_switch(prev_vcpu, next_vcpu);
    
        ...
        schedule_tail(prev_vcpu):
            Save and restore vCPU's CSRs.
    The Xen-saved context allows __context_switch() to switch execution
    from the previous vCPUâ??s stack to the next vCPUâ??s stack and later resume
    execution on the original stack when switching back.
    
    During vCPU creation, the Xen-saved context is going to be initialized
    with:
      - SP pointing to the newly allocated vCPU stack.
      - RA pointing to a helper that performs final vCPU setup before
        transferring control to the guest.
    
    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.
    The prev argument is going to be set by RISC-V ABI (prev will be stored in
    a0) when __context_swtich() will be introduced and called from
    context_switch().
    
    Update the STACK_SIZE definition.
    
    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>
    Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/riscv/Makefile              |  1 +
 xen/arch/riscv/domain.c              | 58 ++++++++++++++++++++++++++++++++++++
 xen/arch/riscv/include/asm/config.h  |  2 +-
 xen/arch/riscv/include/asm/current.h |  6 ++++
 xen/arch/riscv/include/asm/domain.h  | 24 +++++++++++++++
 xen/arch/riscv/stubs.c               | 10 -------
 6 files changed, 90 insertions(+), 11 deletions(-)

diff --git a/xen/arch/riscv/Makefile b/xen/arch/riscv/Makefile
index 1eb9ab090b..caa1aac5b2 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 0000000000..b60320b90d
--- /dev/null
+++ b/xen/arch/riscv/domain.c
@@ -0,0 +1,58 @@
+/* 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");
+}
+
+int arch_vcpu_create(struct vcpu *v)
+{
+    int rc;
+    void *stack = vzalloc(STACK_SIZE);
+
+    if ( !stack )
+        return -ENOMEM;
+
+    v->arch.cpu_info = stack + STACK_SIZE - 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 0;
+
+    /*
+     * 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((void *)&v->arch.cpu_info[1] - STACK_SIZE);
+}
+
+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));
+}
diff --git a/xen/arch/riscv/include/asm/config.h 
b/xen/arch/riscv/include/asm/config.h
index 1e08d3bf78..0613de008b 100644
--- a/xen/arch/riscv/include/asm/config.h
+++ b/xen/arch/riscv/include/asm/config.h
@@ -143,7 +143,7 @@
 
 #define SMP_CACHE_BYTES (1 << 6)
 
-#define STACK_SIZE PAGE_SIZE
+#define STACK_SIZE (PAGE_SIZE << 3)
 
 #define IDENT_AREA_SIZE 64
 
diff --git a/xen/arch/riscv/include/asm/current.h 
b/xen/arch/riscv/include/asm/current.h
index 0c3ea70c2e..58c9f1506b 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 316e7c6c84..f78f145258 100644
--- a/xen/arch/riscv/include/asm/domain.h
+++ b/xen/arch/riscv/include/asm/domain.h
@@ -24,6 +24,30 @@ struct arch_vcpu_io {
 
 struct arch_vcpu {
     struct vcpu_vmid vmid;
+
+    /*
+     * Callee saved registers for Xen's state used to switch from
+     * prev's stack to the next's stack during context switch.
+     */
+    struct
+    {
+        register_t s0;
+        register_t s1;
+        register_t s2;
+        register_t s3;
+        register_t s4;
+        register_t s5;
+        register_t s6;
+        register_t s7;
+        register_t s8;
+        register_t s9;
+        register_t s10;
+        register_t s11;
+        register_t sp;
+        register_t ra;
+    } xen_saved_context;
+
+    struct cpu_info *cpu_info;
 };
 
 struct paging_domain {
diff --git a/xen/arch/riscv/stubs.c b/xen/arch/riscv/stubs.c
index d071c8b86d..daadff0138 100644
--- a/xen/arch/riscv/stubs.c
+++ b/xen/arch/riscv/stubs.c
@@ -116,16 +116,6 @@ 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");
-}
-
 int arch_sanitise_domain_config(struct xen_domctl_createdomain *config)
 {
     BUG_ON("unimplemented");
--
generated by git-patchbot for /home/xen/git/xen.git#staging