xen: make phys_to_machine structure dynamic

We now support the use of memory hotplug, so the physical to machine
page mapping structure must be dynamic.  This is implemented as a
two-level radix tree structure, which allows us to efficiently
incrementally allocate memory for the p2m table as new pages are
added.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

4 files changed, 88 insertions, 3 deletions

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 5c0635a8bffd..73d3c84a3495 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1221,7 +1221,7 @@ asmlinkage void __init xen_start_kernel(void)
 
         /* Get mfn list */
         if (!xen_feature(XENFEAT_auto_translated_physmap))
-                phys_to_machine_mapping = (unsigned long *)xen_start_info->mfn_list;
+                xen_build_dynamic_phys_to_machine();
 
         pgd = (pgd_t *)xen_start_info->pt_base;
 
diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index 07c2653ec335..c3b27dec6f03 100644
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -56,6 +56,91 @@
 #include "multicalls.h"
 #include "mmu.h"
 
+/*
+ * This should probably be a config option.  On 32-bit, it costs 1
+ * page/gig of memory; on 64-bit its 2 pages/gig.  If we want it to be
+ * completely unbounded we can add another level to the p2m structure.
+ */
+#define MAX_GUEST_PAGES         (16ull * 1024*1024*1024 / PAGE_SIZE)
+#define P2M_ENTRIES_PER_PAGE    (PAGE_SIZE / sizeof(unsigned long))
+
+static unsigned long *p2m_top[MAX_GUEST_PAGES / P2M_ENTRIES_PER_PAGE];
+
+static inline unsigned p2m_top_index(unsigned long pfn)
+{
+        BUG_ON(pfn >= MAX_GUEST_PAGES);
+        return pfn / P2M_ENTRIES_PER_PAGE;
+}
+
+static inline unsigned p2m_index(unsigned long pfn)
+{
+        return pfn % P2M_ENTRIES_PER_PAGE;
+}
+
+void __init xen_build_dynamic_phys_to_machine(void)
+{
+        unsigned pfn;
+        unsigned long *mfn_list = (unsigned long *)xen_start_info->mfn_list;
+
+        BUG_ON(xen_start_info->nr_pages >= MAX_GUEST_PAGES);
+
+        for(pfn = 0;
+            pfn < xen_start_info->nr_pages;
+            pfn += P2M_ENTRIES_PER_PAGE) {
+                unsigned topidx = p2m_top_index(pfn);
+
+                p2m_top[topidx] = &mfn_list[pfn];
+        }
+}
+
+unsigned long get_phys_to_machine(unsigned long pfn)
+{
+        unsigned topidx, idx;
+
+        topidx = p2m_top_index(pfn);
+        if (p2m_top[topidx] == NULL)
+                return INVALID_P2M_ENTRY;
+
+        idx = p2m_index(pfn);
+        return p2m_top[topidx][idx];
+}
+
+static void alloc_p2m(unsigned long **pp)
+{
+        unsigned long *p;
+        unsigned i;
+
+        p = (void *)__get_free_page(GFP_KERNEL | __GFP_NOFAIL);
+        BUG_ON(p == NULL);
+
+        for(i = 0; i < P2M_ENTRIES_PER_PAGE; i++)
+                p[i] = INVALID_P2M_ENTRY;
+
+        if (cmpxchg(pp, NULL, p) != NULL)
+                free_page((unsigned long)p);
+}
+
+void set_phys_to_machine(unsigned long pfn, unsigned long mfn)
+{
+        unsigned topidx, idx;
+
+        if (unlikely(xen_feature(XENFEAT_auto_translated_physmap))) {
+                BUG_ON(pfn != mfn && mfn != INVALID_P2M_ENTRY);
+                return;
+        }
+
+        topidx = p2m_top_index(pfn);
+        if (p2m_top[topidx] == NULL) {
+                /* no need to allocate a page to store an invalid entry */
+                if (mfn == INVALID_P2M_ENTRY)
+                        return;
+                alloc_p2m(&p2m_top[topidx]);
+        }
+
+        idx = p2m_index(pfn);
+        p2m_top[topidx][idx] = mfn;
+}
+
 xmaddr_t arbitrary_virt_to_machine(unsigned long address)
 {
         unsigned int level;
diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index 82517e4a752a..37f8f0b8f743 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -27,8 +27,6 @@
 extern const char xen_hypervisor_callback[];
 extern const char xen_failsafe_callback[];
 
-unsigned long *phys_to_machine_mapping;
-EXPORT_SYMBOL(phys_to_machine_mapping);
 
 /**
  * machine_specific_memory_setup - Hook for machine specific memory setup.
diff --git a/arch/x86/xen/xen-ops.h b/arch/x86/xen/xen-ops.h
index f1063ae08037..7bdc8c5c9244 100644
--- a/arch/x86/xen/xen-ops.h
+++ b/arch/x86/xen/xen-ops.h
@@ -22,6 +22,8 @@ void __init xen_arch_setup(void);
 void __init xen_init_IRQ(void);
 void xen_enable_sysenter(void);
 
+void __init xen_build_dynamic_phys_to_machine(void);
+
 void xen_setup_timer(int cpu);
 void xen_setup_cpu_clockevents(void);
 unsigned long xen_cpu_khz(void);