xen/arm: optimize the size of struct vcpu

When CONFIG_NEW_VGIC=y and CONFIG_ARM_64=y, the size of struct vcpu
exceeds one page, which requires allocating two pages and led to the
introduction of MAX_PAGES_PER_VCPU.

To remove the need for MAX_PAGES_PER_VCPU, the vgic member of NEW_VGIC's
struct vgic_cpu member private_irqs is changed to a pointer to struct
vgic_irq.
As a result, the size of struct vcpu for Arm64 is reduced to 2176 bytes
in the case when CONFIG_ARM_64=y and CONFIG_NEW_VGIC=y, compared to 3840
bytes (without these changes and with CONFIG_ARM_64=y) and 4736 bytes
(without these changes and with both CONFIG_ARM_64=y and CONFIG_NEW_VGIC=y).
Note that all numbers are based on defconfig with the mentioned options
enabled or disabled as specified.

Since the private_irqs member is now a pointer, vcpu_vgic_init() and
vcpu_vgic_free() are updated to allocate and free private_irqs instance.

As struct vcpu now fits into one page, drop MAX_PAGES_PER_VCPU.

Suggested-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Michal Orzel <michal.orzel@amd.com>

xen/arch/arm/domain.c

@@ -473,36 +473,21 @@ void dump_pageframe_info(struct domain *d)
 
 }
 
-/*
- * The new VGIC has a bigger per-IRQ structure, so we need more than one
- * page on ARM64. Cowardly increase the limit in this case.
- */
-#if defined(CONFIG_NEW_VGIC) && defined(CONFIG_ARM_64)
-#define MAX_PAGES_PER_VCPU  2
-#else
-#define MAX_PAGES_PER_VCPU  1
-#endif
-
 struct vcpu *alloc_vcpu_struct(const struct domain *d)
 {
     struct vcpu *v;
 
-    BUILD_BUG_ON(sizeof(*v) > MAX_PAGES_PER_VCPU * PAGE_SIZE);
-    v = alloc_xenheap_pages(get_order_from_bytes(sizeof(*v)), 0);
+    BUILD_BUG_ON(sizeof(*v) > PAGE_SIZE);
+    v = alloc_xenheap_page();
     if ( v != NULL )
-    {
-        unsigned int i;
-
-        for ( i = 0; i < DIV_ROUND_UP(sizeof(*v), PAGE_SIZE); i++ )
-            clear_page((void *)v + i * PAGE_SIZE);
-    }
+        clear_page(v);
 
     return v;
 }
 
 void free_vcpu_struct(struct vcpu *v)
 {
-    free_xenheap_pages(v, get_order_from_bytes(sizeof(*v)));
+    free_xenheap_page(v);
 }
 
 int arch_vcpu_create(struct vcpu *v)

xen/arch/arm/include/asm/new_vgic.h

@@ -155,7 +155,7 @@ struct vgic_dist {
 };
 
 struct vgic_cpu {
-    struct vgic_irq private_irqs[VGIC_NR_PRIVATE_IRQS];
+    struct vgic_irq *private_irqs;
 
     struct list_head ap_list_head;
     spinlock_t ap_list_lock;    /* Protects the ap_list */

xen/arch/arm/vgic/vgic-init.c

@@ -202,6 +202,11 @@ int vcpu_vgic_init(struct vcpu *v)
 {
     int ret = 0;
 
+    v->arch.vgic.private_irqs =
+        xzalloc_array(struct vgic_irq, VGIC_NR_PRIVATE_IRQS);
+    if ( !v->arch.vgic.private_irqs )
+        return -ENOMEM;
+
     vgic_vcpu_early_init(v);
 
     if ( gic_hw_version() == GIC_V2 )
@@ -244,6 +249,8 @@ void vcpu_vgic_free(struct vcpu *v)
     struct vgic_cpu *vgic_cpu = &v->arch.vgic;
 
     INIT_LIST_HEAD(&vgic_cpu->ap_list_head);
+
+    XFREE(v->arch.vgic.private_irqs);
 }
 
 /*