xen/riscv: introduce per-vCPU IMSIC state

Each vCPU interacting with the IMSIC requires state to track the
associated guest interrupt file and its backing context.

Introduce a per-vCPU structure to hold IMSIC-related state, including
the guest interrupt file identifier and the CPU providing the backing
VS-file. Access to the guest file identifier is protected by a lock.

Initialize this structure during vCPU setup and store it in arch_vcpu.
The initial state marks the VS-file as software-backed until it becomes
associated with a physical CPU.

Add helper to retrieve the guest interrupt file identifier:
- vcpu_guest_file_id() is going to be used during update of APLIC's
  target register with the pair of information <guest_file_id, cpu_id>
  (to have MSI delivery mode work properly) when guest is trying to
  access vAPLIC's target register.
It will be used in the follow up patches.

Signed-off-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
Acked-by: Jan Beulich <jbeulich@suse.com>

xen/arch/riscv/imsic.c

@@ -16,6 +16,7 @@
 #include <xen/errno.h>
 #include <xen/init.h>
 #include <xen/macros.h>
+#include <xen/sched.h>
 #include <xen/smp.h>
 #include <xen/spinlock.h>
 #include <xen/xvmalloc.h>
@@ -56,6 +57,11 @@ do {                            \
     csr_clear(CSR_SIREG, v);    \
 } while (0)
 
+unsigned int vcpu_guest_file_id(const struct vcpu *v)
+{
+    return ACCESS_ONCE(v->arch.vimsic_state->guest_file_id);
+}
+
 void __init imsic_ids_local_delivery(bool enable)
 {
     if ( enable )
@@ -312,6 +318,35 @@ static int imsic_parse_node(const struct dt_device_node *node,
     return 0;
 }
 
+int vcpu_imsic_init(struct vcpu *v)
+{
+    struct vimsic_state *imsic_state;
+
+    /* Allocate IMSIC context */
+    imsic_state = xvzalloc(struct vimsic_state);
+    if ( !imsic_state )
+        return -ENOMEM;
+
+    /* Setup IMSIC context  */
+    rwlock_init(&imsic_state->vsfile_lock);
+
+    /*
+     * xvzalloc() already cleared the context, so guest_file_id == 0, i.e. the
+     * always-available s/w IMSIC VS-file. Only vsfile_cpu needs an explicit
+     * initializer as its s/w VS-file value is NR_CPUS rather than 0.
+     */
+    imsic_state->vsfile_cpu = NR_CPUS;
+
+    v->arch.vimsic_state = imsic_state;
+
+    return 0;
+}
+
+void vcpu_imsic_deinit(struct vcpu *v)
+{
+    XVFREE(v->arch.vimsic_state);
+}
+
 /*
  * Initialize the imsic_cfg structure based on the IMSIC DT node.
  *

xen/arch/riscv/include/asm/domain.h

@@ -54,6 +54,8 @@ struct arch_vcpu {
 
     struct vtimer vtimer;
 
+    struct vimsic_state *vimsic_state;
+
     register_t hcounteren;
     register_t hedeleg;
     register_t hideleg;

xen/arch/riscv/include/asm/imsic.h

@@ -11,6 +11,7 @@
 #ifndef ASM_RISCV_IMSIC_H
 #define ASM_RISCV_IMSIC_H
 
+#include <xen/rwlock.h>
 #include <xen/spinlock.h>
 #include <xen/stdbool.h>
 #include <xen/types.h>
@@ -61,7 +62,24 @@ struct imsic_config {
     spinlock_t lock;
 };
 
+struct vimsic_state {
+    /* IMSIC VS-file */
+    rwlock_t vsfile_lock;
+    /*
+     * s/w IMSIC VS-file -> guest_file_id == 0
+     * h/w IMSIC VS-file -> guest_file_id > 0
+     */
+    unsigned int guest_file_id;
+    /*
+     * s/w IMSIC VS-file -> vsfile_cpu == NR_CPUS
+     * h/w IMSIC VS-file -> vsfile_cpu < NR_CPUS
+     */
+    unsigned int vsfile_cpu;
+};
+
 struct dt_device_node;
+struct vcpu;
+
 int imsic_init(const struct dt_device_node *node);
 
 const struct imsic_config *imsic_get_config(void);
@@ -71,4 +89,8 @@ void imsic_irq_disable(unsigned int hwirq);
 
 void imsic_ids_local_delivery(bool enable);
 
+int vcpu_imsic_init(struct vcpu *v);
+void vcpu_imsic_deinit(struct vcpu *v);
+unsigned int vcpu_guest_file_id(const struct vcpu *v);
+
 #endif /* ASM_RISCV_IMSIC_H */