[PATCH v2 07/10] xen/arm: Introduce relinquish_p2m_mapping to remove refcount every mapped page

[Julien Grall <julien.grall@linaro.org>]

This function will be called when the domain relinquishes its memory.
It removes refcount on every mapped page to a valid MFN.

Currently, Xen doesn't take refcount on every new mapping but only for foreign
mapping. Restrict the function only on foreign mapping.

Signed-off-by: Julien Grall <julien.grall@linaro.org>

---
    Changes in v2:
        - Introduce the patch
---
 xen/arch/arm/domain.c        |    5 +++++
 xen/arch/arm/p2m.c           |   47 ++++++++++++++++++++++++++++++++++++++++++
 xen/include/asm-arm/domain.h |    1 +
 xen/include/asm-arm/p2m.h    |   15 ++++++++++++++
 4 files changed, 68 insertions(+)

diff --git a/xen/arch/arm/domain.c b/xen/arch/arm/domain.c
index 1590708..e7c2f67 100644
--- a/xen/arch/arm/domain.c
+++ b/xen/arch/arm/domain.c
@@ -717,6 +717,11 @@ int domain_relinquish_resources(struct domain *d)
         if ( ret )
             return ret;
 
+    case RELMEM_mapping:
+        ret = relinquish_p2m_mapping(d);
+        if ( ret )
+            return ret;
+
         d->arch.relmem = RELMEM_done;
         /* Fallthrough */
 
diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
index f0bbaca..dbd6a06 100644
--- a/xen/arch/arm/p2m.c
+++ b/xen/arch/arm/p2m.c
@@ -6,6 +6,7 @@
 #include <xen/bitops.h>
 #include <asm/flushtlb.h>
 #include <asm/gic.h>
+#include <asm/event.h>
 
 /* First level P2M is 2 consecutive pages */
 #define P2M_FIRST_ORDER 1
@@ -320,6 +321,16 @@ static int create_p2m_entries(struct domain *d,
             flush_tlb_all_local();
     }
 
+    if ( (t == p2m_ram_rw) || (t == p2m_ram_ro) || (t == p2m_map_foreign))
+    {
+        unsigned long sgfn = paddr_to_pfn(start_gpaddr);
+        unsigned long egfn = paddr_to_pfn(end_gpaddr);
+
+        p2m->max_mapped_gfn = MAX(p2m->max_mapped_gfn, egfn);
+        /* Use next_gfn_to_relinquish to store the lowest gfn mapped */
+        p2m->next_gfn_to_relinquish = MIN(p2m->next_gfn_to_relinquish, sgfn);
+    }
+
     rc = 0;
 
 out:
@@ -503,12 +514,48 @@ int p2m_init(struct domain *d)
 
     p2m->first_level = NULL;
 
+    p2m->max_mapped_gfn = 0;
+    p2m->next_gfn_to_relinquish = ULONG_MAX;
+
 err:
     spin_unlock(&p2m->lock);
 
     return rc;
 }
 
+int relinquish_p2m_mapping(struct domain *d)
+{
+    struct p2m_domain *p2m = &d->arch.p2m;
+    unsigned long gfn, count = 0;
+    int rc = 0;
+
+    for ( gfn = p2m->next_gfn_to_relinquish;
+          gfn < p2m->max_mapped_gfn; gfn++ )
+    {
+        p2m_type_t t;
+        paddr_t p = p2m_lookup(d, gfn, &t);
+        unsigned long mfn = p >> PAGE_SHIFT;
+
+        if ( mfn_valid(mfn) && p2m_is_foreign(t) )
+        {
+            put_page(mfn_to_page(mfn));
+            guest_physmap_remove_page(d, gfn, mfn, 0);
+        }
+
+        count++;
+
+        /* Preempt every 2MiB. Arbitrary */
+        if ( (count == 512) && hypercall_preempt_check() )
+        {
+            p2m->next_gfn_to_relinquish = gfn + 1;
+            rc = -EAGAIN;
+            break;
+        }
+    }
+
+    return rc;
+}
+
 unsigned long gmfn_to_mfn(struct domain *d, unsigned long gpfn)
 {
     paddr_t p = p2m_lookup(d, pfn_to_paddr(gpfn), NULL);
diff --git a/xen/include/asm-arm/domain.h b/xen/include/asm-arm/domain.h
index 922eda3..4a4c018 100644
--- a/xen/include/asm-arm/domain.h
+++ b/xen/include/asm-arm/domain.h
@@ -75,6 +75,7 @@ struct arch_domain
         RELMEM_not_started,
         RELMEM_xen,
         RELMEM_page,
+        RELMEM_mapping,
         RELMEM_done,
     } relmem;
 
diff --git a/xen/include/asm-arm/p2m.h b/xen/include/asm-arm/p2m.h
index b63204d..b0d3aea 100644
--- a/xen/include/asm-arm/p2m.h
+++ b/xen/include/asm-arm/p2m.h
@@ -18,6 +18,15 @@ struct p2m_domain {
 
     /* Current VMID in use */
     uint8_t vmid;
+
+    /* Highest guest frame that's ever been mapped in the p2m
+     * Take only into account ram and foreign mapping
+     */
+    unsigned long max_mapped_gfn;
+
+    /* When releasing mapped gfn's in a preemptible manner, recall where
+     * to resume the search */
+    unsigned long next_gfn_to_relinquish;
 };
 
 /* List of possible type for each page in the p2m
@@ -48,6 +57,12 @@ int p2m_init(struct domain *d);
 /* Return all the p2m resources to Xen. */
 void p2m_teardown(struct domain *d);
 
+/* Remove mapping refcount on each mapping page in the p2m
+ *
+ * TODO: For the moment only foreign mapping is handled
+ */
+int relinquish_p2m_mapping(struct domain *d);
+
 /* Allocate a new p2m table for a domain.
  *
  * Returns 0 for success or -errno.
-- 
1.7.10.4