[Xen-devel] [PATCH 05/11] xen: add m2p override mechanism

[stefano.stabellini@xxxxxxxxxxxxx]

From: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>

Add a simple hashtable based mechanism to override some portions of the
m2p, so that we can find out the pfn corresponding to an mfn of a
granted page. In fact entries corresponding to granted pages in the m2p
hold the original pfn value of the page in the source domain that
granted it.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>
Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
---
 arch/x86/include/asm/xen/page.h |   16 ++++++-
 arch/x86/xen/p2m.c              |   80 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 93 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/xen/page.h b/arch/x86/include/asm/xen/page.h
index 8760cc6..50f0a0f 100644
--- a/arch/x86/include/asm/xen/page.h
+++ b/arch/x86/include/asm/xen/page.h
@@ -42,6 +42,11 @@ extern unsigned int   machine_to_phys_order;
 extern unsigned long get_phys_to_machine(unsigned long pfn);
 extern bool set_phys_to_machine(unsigned long pfn, unsigned long mfn);
 
+extern void m2p_add_override(unsigned long mfn, struct page *page);
+extern void m2p_remove_override(struct page *page);
+extern struct page *m2p_find_override(unsigned long mfn);
+extern unsigned long m2p_find_override_pfn(unsigned long mfn, unsigned long 
pfn);
+
 static inline unsigned long pfn_to_mfn(unsigned long pfn)
 {
        unsigned long mfn;
@@ -72,9 +77,6 @@ static inline unsigned long mfn_to_pfn(unsigned long mfn)
        if (xen_feature(XENFEAT_auto_translated_physmap))
                return mfn;
 
-       if (unlikely((mfn >> machine_to_phys_order) != 0))
-               return ~0;
-
        pfn = 0;
        /*
         * The array access can fail (e.g., device space beyond end of RAM).
@@ -83,6 +85,14 @@ static inline unsigned long mfn_to_pfn(unsigned long mfn)
         */
        __get_user(pfn, &machine_to_phys_mapping[mfn]);
 
+       /*
+        * If this appears to be a foreign mfn (because the pfn
+        * doesn't map back to the mfn), then check the local override
+        * table to see if there's a better pfn to use.
+        */
+       if (get_phys_to_machine(pfn) != mfn)
+               pfn = m2p_find_override_pfn(mfn, pfn);
+
        return pfn;
 }
 
diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
index 259ec3b..8db19d5 100644
--- a/arch/x86/xen/p2m.c
+++ b/arch/x86/xen/p2m.c
@@ -27,6 +27,8 @@
 
 #include <linux/init.h>
 #include <linux/module.h>
+#include <linux/list.h>
+#include <linux/hash.h>
 
 #include <asm/cache.h>
 #include <asm/setup.h>
@@ -37,6 +39,8 @@
 
 #include "xen-ops.h"
 
+static void __init m2p_override_init(void);
+
 unsigned long xen_max_p2m_pfn __read_mostly;
 
 #define P2M_PER_PAGE           (PAGE_SIZE / sizeof(unsigned long))
@@ -234,6 +238,8 @@ void __init xen_build_dynamic_phys_to_machine(void)
 
                p2m_top[topidx][mididx] = &mfn_list[pfn];
        }
+
+       m2p_override_init();
 }
 
 unsigned long get_phys_to_machine(unsigned long pfn)
@@ -374,3 +380,77 @@ bool set_phys_to_machine(unsigned long pfn, unsigned long 
mfn)
 
        return true;
 }
+
+#define M2P_OVERRIDE_HASH_SHIFT        10
+#define M2P_OVERRIDE_HASH      (1 << M2P_OVERRIDE_HASH_SHIFT)
+
+static RESERVE_BRK_ARRAY(struct list_head, m2p_overrides, M2P_OVERRIDE_HASH);
+static DEFINE_SPINLOCK(m2p_override_lock);
+
+static void __init m2p_override_init(void)
+{
+       unsigned i;
+
+       m2p_overrides = extend_brk(sizeof(*m2p_overrides) * M2P_OVERRIDE_HASH,
+                                  sizeof(unsigned long));
+
+       for (i = 0; i < M2P_OVERRIDE_HASH; i++)
+               INIT_LIST_HEAD(&m2p_overrides[i]);
+}
+
+static unsigned long mfn_hash(unsigned long mfn)
+{
+       return hash_long(mfn, M2P_OVERRIDE_HASH_SHIFT);
+}
+
+/* Add an MFN override for a particular page */
+void m2p_add_override(unsigned long mfn, struct page *page)
+{
+       unsigned long flags;
+       page->private = mfn;
+
+       spin_lock_irqsave(&m2p_override_lock, flags);
+       list_add(&page->lru,  &m2p_overrides[mfn_hash(mfn)]);
+       spin_unlock_irqrestore(&m2p_override_lock, flags);
+}
+
+void m2p_remove_override(struct page *page)
+{
+       unsigned long flags;
+       spin_lock_irqsave(&m2p_override_lock, flags);
+       list_del(&page->lru);
+       spin_unlock_irqrestore(&m2p_override_lock, flags);
+}
+
+struct page *m2p_find_override(unsigned long mfn)
+{
+       unsigned long flags;
+       struct list_head *bucket = &m2p_overrides[mfn_hash(mfn)];
+       struct page *p, *ret;
+
+       ret = NULL;
+
+       spin_lock_irqsave(&m2p_override_lock, flags);
+
+       list_for_each_entry(p, bucket, lru) {
+               if (p->private == mfn) {
+                       ret = p;
+                       break;
+               }
+       }
+
+       spin_unlock_irqrestore(&m2p_override_lock, flags);
+
+       return ret;
+}
+
+unsigned long m2p_find_override_pfn(unsigned long mfn, unsigned long pfn)
+{
+       struct page *p = m2p_find_override(mfn);
+       unsigned long ret = pfn;
+
+       if (p)
+               ret = page_to_pfn(p);
+
+       return ret;
+}
-- 
1.5.6.5


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