[PATCH v2 04/17] xen/riscv: construct the P2M pages pool for guests

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

Implement p2m_set_allocation() to construct p2m pages pool for guests
based on required number of pages.

This is implemented by:
- Adding a `struct paging_domain` which contains a freelist, a
  counter variable and a spinlock to `struct arch_domain` to
  indicate the free p2m pages and the number of p2m total pages in
  the p2m pages pool.
- Adding a helper `p2m_set_allocation` to set the p2m pages pool
  size. This helper should be called before allocating memory for
  a guest and is called from domain_p2m_set_allocation(), the latter
  is a part of common dom0less code.

Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
---
Changes in v2:
 - Drop the comment above inclusion of <xen/event.h> in riscv/p2m.c.
 - Use ACCESS_ONCE() for lhs and rhs for the expressions in
   p2m_set_allocation().
---
 xen/arch/riscv/include/asm/domain.h | 12 ++++++
 xen/arch/riscv/p2m.c                | 59 +++++++++++++++++++++++++++++
 2 files changed, 71 insertions(+)

diff --git a/xen/arch/riscv/include/asm/domain.h 
b/xen/arch/riscv/include/asm/domain.h
index b9a03e91c5..b818127f9f 100644
--- a/xen/arch/riscv/include/asm/domain.h
+++ b/xen/arch/riscv/include/asm/domain.h
@@ -2,6 +2,8 @@
 #ifndef ASM__RISCV__DOMAIN_H
 #define ASM__RISCV__DOMAIN_H
 
+#include <xen/mm.h>
+#include <xen/spinlock.h>
 #include <xen/xmalloc.h>
 #include <public/hvm/params.h>
 
@@ -18,10 +20,20 @@ struct arch_vcpu_io {
 struct arch_vcpu {
 };
 
+struct paging_domain {
+    spinlock_t lock;
+    /* Free P2M pages from the pre-allocated P2M pool */
+    struct page_list_head p2m_freelist;
+    /* Number of pages from the pre-allocated P2M pool */
+    unsigned long p2m_total_pages;
+};
+
 struct arch_domain {
     struct hvm_domain hvm;
 
     struct p2m_domain p2m;
+
+    struct paging_domain paging;
 };
 
 #include <xen/sched.h>
diff --git a/xen/arch/riscv/p2m.c b/xen/arch/riscv/p2m.c
index 9f7fd8290a..f33c7147ff 100644
--- a/xen/arch/riscv/p2m.c
+++ b/xen/arch/riscv/p2m.c
@@ -1,4 +1,5 @@
 #include <xen/bitops.h>
+#include <xen/event.h>
 #include <xen/lib.h>
 #include <xen/sched.h>
 #include <xen/spinlock.h>
@@ -105,6 +106,9 @@ int p2m_init(struct domain *d)
     struct p2m_domain *p2m = p2m_get_hostp2m(d);
     int rc;
 
+    spin_lock_init(&d->arch.paging.lock);
+    INIT_PAGE_LIST_HEAD(&d->arch.paging.p2m_freelist);
+
     p2m->vmid = INVALID_VMID;
 
     rc = p2m_alloc_vmid(d);
@@ -113,3 +117,58 @@ int p2m_init(struct domain *d)
 
     return 0;
 }
+
+/*
+ * Set the pool of pages to the required number of pages.
+ * Returns 0 for success, non-zero for failure.
+ * Call with d->arch.paging.lock held.
+ */
+int p2m_set_allocation(struct domain *d, unsigned long pages, bool *preempted)
+{
+    struct page_info *pg;
+
+    ASSERT(spin_is_locked(&d->arch.paging.lock));
+
+    for ( ; ; )
+    {
+        if ( d->arch.paging.p2m_total_pages < pages )
+        {
+            /* Need to allocate more memory from domheap */
+            pg = alloc_domheap_page(d, MEMF_no_owner);
+            if ( pg == NULL )
+            {
+                printk(XENLOG_ERR "Failed to allocate P2M pages.\n");
+                return -ENOMEM;
+            }
+            ACCESS_ONCE(d->arch.paging.p2m_total_pages)++;
+            page_list_add_tail(pg, &d->arch.paging.p2m_freelist);
+        }
+        else if ( d->arch.paging.p2m_total_pages > pages )
+        {
+            /* Need to return memory to domheap */
+            pg = page_list_remove_head(&d->arch.paging.p2m_freelist);
+            if( pg )
+            {
+                ACCESS_ONCE(d->arch.paging.p2m_total_pages)--;
+                free_domheap_page(pg);
+            }
+            else
+            {
+                printk(XENLOG_ERR
+                       "Failed to free P2M pages, P2M freelist is empty.\n");
+                return -ENOMEM;
+            }
+        }
+        else
+            break;
+
+        /* Check to see if we need to yield and try again */
+        if ( preempted && general_preempt_check() )
+        {
+            *preempted = true;
+            return -ERESTART;
+        }
+    }
+
+    return 0;
+}
-- 
2.49.0