6 files changed, 499 insertions, 22 deletions
diff --git a/arch/x86/include/asm/xen/page.h b/arch/x86/include/asm/xen/page.h
index f25bdf238a33..c61934fbf22a 100644
--- a/arch/x86/include/asm/xen/page.h
+++ b/arch/x86/include/asm/xen/page.h
@@ -29,8 +29,10 @@ typedef struct xpaddr {
 /**** MACHINE <-> PHYSICAL CONVERSION MACROS ****/
 #define INVALID_P2M_ENTRY       (~0UL)
-#define FOREIGN_FRAME_BIT       (1UL<<31)
+#define FOREIGN_FRAME_BIT       (1UL<<(BITS_PER_LONG-1))
+#define IDENTITY_FRAME_BIT      (1UL<<(BITS_PER_LONG-2))
 #define FOREIGN_FRAME(m)        ((m) | FOREIGN_FRAME_BIT)
+#define IDENTITY_FRAME(m)       ((m) | IDENTITY_FRAME_BIT)
 /* Maximum amount of memory we can handle in a domain in pages */
 #define MAX_DOMAIN_PAGES                                                \
@@ -41,12 +43,18 @@ 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 bool __set_phys_to_machine(unsigned long pfn, unsigned long mfn);
+extern unsigned long set_phys_range_identity(unsigned long pfn_s,
+                                             unsigned long pfn_e);
 extern int m2p_add_override(unsigned long mfn, struct page *page);
 extern int 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);
+#ifdef CONFIG_XEN_DEBUG_FS
+extern int p2m_dump_show(struct seq_file *m, void *v);
+#endif
 static inline unsigned long pfn_to_mfn(unsigned long pfn)
 {
        unsigned long mfn;
@@ -57,7 +65,7 @@ static inline unsigned long pfn_to_mfn(unsigned long pfn)
        mfn = get_phys_to_machine(pfn);
        if (mfn != INVALID_P2M_ENTRY)
-                mfn &= ~FOREIGN_FRAME_BIT;
+                mfn &= ~(FOREIGN_FRAME_BIT | IDENTITY_FRAME_BIT);
        return mfn;
 }
@@ -73,25 +81,44 @@ static inline int phys_to_machine_mapping_valid(unsigned long pfn)
 static inline unsigned long mfn_to_pfn(unsigned long mfn)
 {
        unsigned long pfn;
+        int ret = 0;
        if (xen_feature(XENFEAT_auto_translated_physmap))
                return mfn;
+        if (unlikely((mfn >> machine_to_phys_order) != 0)) {
+                pfn = ~0;
+                goto try_override;
+        }
        pfn = 0;
        /*
         * The array access can fail (e.g., device space beyond end of RAM).
         * In such cases it doesn't matter what we return (we return garbage),
         * but we must handle the fault without crashing!
         */
-        __get_user(pfn, &machine_to_phys_mapping[mfn]);
+        ret = __get_user(pfn, &machine_to_phys_mapping[mfn]);
+try_override:
-        /*
+        /* ret might be < 0 if there are no entries in the m2p for mfn */
-         * If this appears to be a foreign mfn (because the pfn
+        if (ret < 0)
-         * doesn't map back to the mfn), then check the local override
+                pfn = ~0;
-         * table to see if there's a better pfn to use.
+        else if (get_phys_to_machine(pfn) != 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.
+                 *
+                 * m2p_find_override_pfn returns ~0 if it doesn't find anything.
+                 */
+                pfn = m2p_find_override_pfn(mfn, ~0);
+        /* 
+         * pfn is ~0 if there are no entries in the m2p for mfn or if the
+         * entry doesn't map back to the mfn and m2p_override doesn't have a
+         * valid entry for it.
         */
-        if (get_phys_to_machine(pfn) != mfn)
+        if (pfn == ~0 &&
-                pfn = m2p_find_override_pfn(mfn, pfn);
+                        get_phys_to_machine(mfn) == IDENTITY_FRAME(mfn))
+                pfn = mfn;
        return pfn;
 }
diff --git a/arch/x86/xen/Kconfig b/arch/x86/xen/Kconfig
index 5b54892e4bc3..e4343fe488ed 100644
--- a/arch/x86/xen/Kconfig
+++ b/arch/x86/xen/Kconfig
@@ -48,3 +48,11 @@ config XEN_DEBUG_FS
        help
          Enable statistics output and various tuning options in debugfs.
          Enabling this option may incur a significant performance overhead.
+config XEN_DEBUG
+        bool "Enable Xen debug checks"
+        depends on XEN
+        default n
+        help
+          Enable various WARN_ON checks in the Xen MMU code.
+          Enabling this option WILL incur a significant performance overhead.
diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index f6089421147a..832765c0fb8c 100644
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -46,6 +46,7 @@
 #include <linux/module.h>
 #include <linux/gfp.h>
 #include <linux/memblock.h>
+#include <linux/seq_file.h>
 #include <asm/pgtable.h>
 #include <asm/tlbflush.h>
@@ -416,8 +417,12 @@ static pteval_t pte_pfn_to_mfn(pteval_t val)
        if (val & _PAGE_PRESENT) {
                unsigned long pfn = (val & PTE_PFN_MASK) >> PAGE_SHIFT;
                pteval_t flags = val & PTE_FLAGS_MASK;
-                unsigned long mfn = pfn_to_mfn(pfn);
+                unsigned long mfn;
+                if (!xen_feature(XENFEAT_auto_translated_physmap))
+                        mfn = get_phys_to_machine(pfn);
+                else
+                        mfn = pfn;
                /*
                 * If there's no mfn for the pfn, then just create an
                 * empty non-present pte.  Unfortunately this loses
@@ -427,8 +432,18 @@ static pteval_t pte_pfn_to_mfn(pteval_t val)
                if (unlikely(mfn == INVALID_P2M_ENTRY)) {
                        mfn = 0;
                        flags = 0;
+                } else {
+                        /*
+                         * Paramount to do this test _after_ the
+                         * INVALID_P2M_ENTRY as INVALID_P2M_ENTRY &
+                         * IDENTITY_FRAME_BIT resolves to true.
+                         */
+                        mfn &= ~FOREIGN_FRAME_BIT;
+                        if (mfn & IDENTITY_FRAME_BIT) {
+                                mfn &= ~IDENTITY_FRAME_BIT;
+                                flags |= _PAGE_IOMAP;
+                        }
                }
                val = ((pteval_t)mfn << PAGE_SHIFT) | flags;
        }
@@ -532,6 +547,41 @@ pte_t xen_make_pte(pteval_t pte)
 }
 PV_CALLEE_SAVE_REGS_THUNK(xen_make_pte);
+#ifdef CONFIG_XEN_DEBUG
+pte_t xen_make_pte_debug(pteval_t pte)
+{
+        phys_addr_t addr = (pte & PTE_PFN_MASK);
+        phys_addr_t other_addr;
+        bool io_page = false;
+        pte_t _pte;
+        if (pte & _PAGE_IOMAP)
+                io_page = true;
+        _pte = xen_make_pte(pte);
+        if (!addr)
+                return _pte;
+        if (io_page &&
+            (xen_initial_domain() || addr >= ISA_END_ADDRESS)) {
+                other_addr = pfn_to_mfn(addr >> PAGE_SHIFT) << PAGE_SHIFT;
+                WARN(addr != other_addr,
+                        "0x%lx is using VM_IO, but it is 0x%lx!\n",
+                        (unsigned long)addr, (unsigned long)other_addr);
+        } else {
+                pteval_t iomap_set = (_pte.pte & PTE_FLAGS_MASK) & _PAGE_IOMAP;
+                other_addr = (_pte.pte & PTE_PFN_MASK);
+                WARN((addr == other_addr) && (!io_page) && (!iomap_set),
+                        "0x%lx is missing VM_IO (and wasn't fixed)!\n",
+                        (unsigned long)addr);
+        }
+        return _pte;
+}
+PV_CALLEE_SAVE_REGS_THUNK(xen_make_pte_debug);
+#endif
 pgd_t xen_make_pgd(pgdval_t pgd)
 {
        pgd = pte_pfn_to_mfn(pgd);
@@ -1940,6 +1990,9 @@ __init void xen_ident_map_ISA(void)
 static __init void xen_post_allocator_init(void)
 {
+#ifdef CONFIG_XEN_DEBUG
+        pv_mmu_ops.make_pte = PV_CALLEE_SAVE(xen_make_pte_debug);
+#endif
        pv_mmu_ops.set_pte = xen_set_pte;
        pv_mmu_ops.set_pmd = xen_set_pmd;
        pv_mmu_ops.set_pud = xen_set_pud;
@@ -2072,7 +2125,7 @@ static void xen_zap_pfn_range(unsigned long vaddr, unsigned int order,
                        in_frames[i] = virt_to_mfn(vaddr);
                MULTI_update_va_mapping(mcs.mc, vaddr, VOID_PTE, 0);
-                set_phys_to_machine(virt_to_pfn(vaddr), INVALID_P2M_ENTRY);
+                __set_phys_to_machine(virt_to_pfn(vaddr), INVALID_P2M_ENTRY);
                if (out_frames)
                        out_frames[i] = virt_to_pfn(vaddr);
@@ -2351,6 +2404,18 @@ EXPORT_SYMBOL_GPL(xen_remap_domain_mfn_range);
 #ifdef CONFIG_XEN_DEBUG_FS
+static int p2m_dump_open(struct inode *inode, struct file *filp)
+{
+        return single_open(filp, p2m_dump_show, NULL);
+}
+static const struct file_operations p2m_dump_fops = {
+        .open           = p2m_dump_open,
+        .read           = seq_read,
+        .llseek         = seq_lseek,
+        .release        = single_release,
+};
 static struct dentry *d_mmu_debug;
 static int __init xen_mmu_debugfs(void)
@@ -2406,6 +2471,7 @@ static int __init xen_mmu_debugfs(void)
        debugfs_create_u32("prot_commit_batched", 0444, d_mmu_debug,
                           &mmu_stats.prot_commit_batched);
+        debugfs_create_file("p2m", 0600, d_mmu_debug, NULL, &p2m_dump_fops);
        return 0;
 }
 fs_initcall(xen_mmu_debugfs);
diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
index fd12d7ce7ff9..00fe5604c593 100644
--- a/arch/x86/xen/p2m.c
+++ b/arch/x86/xen/p2m.c
@@ -23,6 +23,129 @@
 * P2M_PER_PAGE depends on the architecture, as a mfn is always
 * unsigned long (8 bytes on 64-bit, 4 bytes on 32), leading to
 * 512 and 1024 entries respectively. 
+ *
+ * In short, these structures contain the Machine Frame Number (MFN) of the PFN.
+ *
+ * However not all entries are filled with MFNs. Specifically for all other
+ * leaf entries, or for the top  root, or middle one, for which there is a void
+ * entry, we assume it is  "missing". So (for example)
+ *  pfn_to_mfn(0x90909090)=INVALID_P2M_ENTRY.
+ *
+ * We also have the possibility of setting 1-1 mappings on certain regions, so
+ * that:
+ *  pfn_to_mfn(0xc0000)=0xc0000
+ *
+ * The benefit of this is, that we can assume for non-RAM regions (think
+ * PCI BARs, or ACPI spaces), we can create mappings easily b/c we
+ * get the PFN value to match the MFN.
+ *
+ * For this to work efficiently we have one new page p2m_identity and
+ * allocate (via reserved_brk) any other pages we need to cover the sides
+ * (1GB or 4MB boundary violations). All entries in p2m_identity are set to
+ * INVALID_P2M_ENTRY type (Xen toolstack only recognizes that and MFNs,
+ * no other fancy value).
+ *
+ * On lookup we spot that the entry points to p2m_identity and return the
+ * identity value instead of dereferencing and returning INVALID_P2M_ENTRY.
+ * If the entry points to an allocated page, we just proceed as before and
+ * return the PFN.  If the PFN has IDENTITY_FRAME_BIT set we unmask that in
+ * appropriate functions (pfn_to_mfn).
+ *
+ * The reason for having the IDENTITY_FRAME_BIT instead of just returning the
+ * PFN is that we could find ourselves where pfn_to_mfn(pfn)==pfn for a
+ * non-identity pfn. To protect ourselves against we elect to set (and get) the
+ * IDENTITY_FRAME_BIT on all identity mapped PFNs.
+ *
+ * This simplistic diagram is used to explain the more subtle piece of code.
+ * There is also a digram of the P2M at the end that can help.
+ * Imagine your E820 looking as so:
+ *
+ *                    1GB                                           2GB
+ * /-------------------+---------\/----\         /----------\    /---+-----\
+ * | System RAM        | Sys RAM ||ACPI|         | reserved |    | Sys RAM |
+ * \-------------------+---------/\----/         \----------/    \---+-----/
+ *                               ^- 1029MB                       ^- 2001MB
+ *
+ * [1029MB = 263424 (0x40500), 2001MB = 512256 (0x7D100),
+ *  2048MB = 524288 (0x80000)]
+ *
+ * And dom0_mem=max:3GB,1GB is passed in to the guest, meaning memory past 1GB
+ * is actually not present (would have to kick the balloon driver to put it in).
+ *
+ * When we are told to set the PFNs for identity mapping (see patch: "xen/setup:
+ * Set identity mapping for non-RAM E820 and E820 gaps.") we pass in the start
+ * of the PFN and the end PFN (263424 and 512256 respectively). The first step
+ * is to reserve_brk a top leaf page if the p2m[1] is missing. The top leaf page
+ * covers 512^2 of page estate (1GB) and in case the start or end PFN is not
+ * aligned on 512^2*PAGE_SIZE (1GB) we loop on aligned 1GB PFNs from start pfn
+ * to end pfn.  We reserve_brk top leaf pages if they are missing (means they
+ * point to p2m_mid_missing).
+ *
+ * With the E820 example above, 263424 is not 1GB aligned so we allocate a
+ * reserve_brk page which will cover the PFNs estate from 0x40000 to 0x80000.
+ * Each entry in the allocate page is "missing" (points to p2m_missing).
+ *
+ * Next stage is to determine if we need to do a more granular boundary check
+ * on the 4MB (or 2MB depending on architecture) off the start and end pfn's.
+ * We check if the start pfn and end pfn violate that boundary check, and if
+ * so reserve_brk a middle (p2m[x][y]) leaf page. This way we have a much finer
+ * granularity of setting which PFNs are missing and which ones are identity.
+ * In our example 263424 and 512256 both fail the check so we reserve_brk two
+ * pages. Populate them with INVALID_P2M_ENTRY (so they both have "missing"
+ * values) and assign them to p2m[1][2] and p2m[1][488] respectively.
+ *
+ * At this point we would at minimum reserve_brk one page, but could be up to
+ * three. Each call to set_phys_range_identity has at maximum a three page
+ * cost. If we were to query the P2M at this stage, all those entries from
+ * start PFN through end PFN (so 1029MB -> 2001MB) would return
+ * INVALID_P2M_ENTRY ("missing").
+ *
+ * The next step is to walk from the start pfn to the end pfn setting
+ * the IDENTITY_FRAME_BIT on each PFN. This is done in set_phys_range_identity.
+ * If we find that the middle leaf is pointing to p2m_missing we can swap it
+ * over to p2m_identity - this way covering 4MB (or 2MB) PFN space.  At this
+ * point we do not need to worry about boundary aligment (so no need to
+ * reserve_brk a middle page, figure out which PFNs are "missing" and which
+ * ones are identity), as that has been done earlier.  If we find that the
+ * middle leaf is not occupied by p2m_identity or p2m_missing, we dereference
+ * that page (which covers 512 PFNs) and set the appropriate PFN with
+ * IDENTITY_FRAME_BIT. In our example 263424 and 512256 end up there, and we
+ * set from p2m[1][2][256->511] and p2m[1][488][0->256] with
+ * IDENTITY_FRAME_BIT set.
+ *
+ * All other regions that are void (or not filled) either point to p2m_missing
+ * (considered missing) or have the default value of INVALID_P2M_ENTRY (also
+ * considered missing). In our case, p2m[1][2][0->255] and p2m[1][488][257->511]
+ * contain the INVALID_P2M_ENTRY value and are considered "missing."
+ *
+ * This is what the p2m ends up looking (for the E820 above) with this
+ * fabulous drawing:
+ *
+ *    p2m         /--------------\
+ *  /-----\       | &mfn_list[0],|                           /-----------------\
+ *  |  0  |------>| &mfn_list[1],|    /---------------\      | ~0, ~0, ..      |
+ *  |-----|       |  ..., ~0, ~0 |    | ~0, ~0, [x]---+----->| IDENTITY [@256] |
+ *  |  1  |---\   \--------------/    | [p2m_identity]+\     | IDENTITY [@257] |
+ *  |-----|    \                      | [p2m_identity]+\\    | ....            |
+ *  |  2  |--\  \-------------------->|  ...          | \\   \----------------/
+ *  |-----|   \                       \---------------/  \\
+ *  |  3  |\   \                                          \\  p2m_identity
+ *  |-----| \   \-------------------->/---------------\   /-----------------\
+ *  | ..  +->+                        | [p2m_identity]+-->| ~0, ~0, ~0, ... |
+ *  \-----/ /                         | [p2m_identity]+-->| ..., ~0         |
+ *         / /---------------\        | ....          |   \-----------------/
+ *        /  | IDENTITY[@0]  |      /-+-[x], ~0, ~0.. |
+ *       /   | IDENTITY[@256]|<----/  \---------------/
+ *      /    | ~0, ~0, ....  |
+ *     |     \---------------/
+ *     |
+ *     p2m_missing             p2m_missing
+ * /------------------\     /------------\
+ * | [p2m_mid_missing]+---->| ~0, ~0, ~0 |
+ * | [p2m_mid_missing]+---->| ..., ~0    |
+ * \------------------/     \------------/
+ *
+ * where ~0 is INVALID_P2M_ENTRY. IDENTITY is (PFN | IDENTITY_BIT)
 */
 #include <linux/init.h>
@@ -30,6 +153,7 @@
 #include <linux/list.h>
 #include <linux/hash.h>
 #include <linux/sched.h>
+#include <linux/seq_file.h>
 #include <asm/cache.h>
 #include <asm/setup.h>
@@ -59,9 +183,15 @@ static RESERVE_BRK_ARRAY(unsigned long **, p2m_top, P2M_TOP_PER_PAGE);
 static RESERVE_BRK_ARRAY(unsigned long, p2m_top_mfn, P2M_TOP_PER_PAGE);
 static RESERVE_BRK_ARRAY(unsigned long *, p2m_top_mfn_p, P2M_TOP_PER_PAGE);
+static RESERVE_BRK_ARRAY(unsigned long, p2m_identity, P2M_PER_PAGE);
 RESERVE_BRK(p2m_mid, PAGE_SIZE * (MAX_DOMAIN_PAGES / (P2M_PER_PAGE * P2M_MID_PER_PAGE)));
 RESERVE_BRK(p2m_mid_mfn, PAGE_SIZE * (MAX_DOMAIN_PAGES / (P2M_PER_PAGE * P2M_MID_PER_PAGE)));
+/* We might hit two boundary violations at the start and end, at max each
+ * boundary violation will require three middle nodes. */
+RESERVE_BRK(p2m_mid_identity, PAGE_SIZE * 2 * 3);
 static inline unsigned p2m_top_index(unsigned long pfn)
 {
        BUG_ON(pfn >= MAX_P2M_PFN);
@@ -221,6 +351,9 @@ void __init xen_build_dynamic_phys_to_machine(void)
        p2m_top = extend_brk(PAGE_SIZE, PAGE_SIZE);
        p2m_top_init(p2m_top);
+        p2m_identity = extend_brk(PAGE_SIZE, PAGE_SIZE);
+        p2m_init(p2m_identity);
        /*
         * The domain builder gives us a pre-constructed p2m array in
         * mfn_list for all the pages initially given to us, so we just
@@ -266,6 +399,14 @@ unsigned long get_phys_to_machine(unsigned long pfn)
        mididx = p2m_mid_index(pfn);
        idx = p2m_index(pfn);
+        /*
+         * The INVALID_P2M_ENTRY is filled in both p2m_*identity
+         * and in p2m_*missing, so returning the INVALID_P2M_ENTRY
+         * would be wrong.
+         */
+        if (p2m_top[topidx][mididx] == p2m_identity)
+                return IDENTITY_FRAME(pfn);
        return p2m_top[topidx][mididx][idx];
 }
 EXPORT_SYMBOL_GPL(get_phys_to_machine);
@@ -335,9 +476,11 @@ static bool alloc_p2m(unsigned long pfn)
                        p2m_top_mfn_p[topidx] = mid_mfn;
        }
-        if (p2m_top[topidx][mididx] == p2m_missing) {
+        if (p2m_top[topidx][mididx] == p2m_identity ||
+            p2m_top[topidx][mididx] == p2m_missing) {
                /* p2m leaf page is missing */
                unsigned long *p2m;
+                unsigned long *p2m_orig = p2m_top[topidx][mididx];
                p2m = alloc_p2m_page();
                if (!p2m)
@@ -345,7 +488,7 @@ static bool alloc_p2m(unsigned long pfn)
                p2m_init(p2m);
-                if (cmpxchg(&mid[mididx], p2m_missing, p2m) != p2m_missing)
+                if (cmpxchg(&mid[mididx], p2m_orig, p2m) != p2m_orig)
                        free_p2m_page(p2m);
                else
                        mid_mfn[mididx] = virt_to_mfn(p2m);
@@ -354,11 +497,91 @@ static bool alloc_p2m(unsigned long pfn)
        return true;
 }
+bool __early_alloc_p2m(unsigned long pfn)
+{
+        unsigned topidx, mididx, idx;
+        topidx = p2m_top_index(pfn);
+        mididx = p2m_mid_index(pfn);
+        idx = p2m_index(pfn);
+        /* Pfff.. No boundary cross-over, lets get out. */
+        if (!idx)
+                return false;
+        WARN(p2m_top[topidx][mididx] == p2m_identity,
+                "P2M[%d][%d] == IDENTITY, should be MISSING (or alloced)!\n",
+                topidx, mididx);
+        /*
+         * Could be done by xen_build_dynamic_phys_to_machine..
+         */
+        if (p2m_top[topidx][mididx] != p2m_missing)
+                return false;
+        /* Boundary cross-over for the edges: */
+        if (idx) {
+                unsigned long *p2m = extend_brk(PAGE_SIZE, PAGE_SIZE);
+                p2m_init(p2m);
+                p2m_top[topidx][mididx] = p2m;
+        }
+        return idx != 0;
+}
+unsigned long set_phys_range_identity(unsigned long pfn_s,
+                                      unsigned long pfn_e)
+{
+        unsigned long pfn;
+        if (unlikely(pfn_s >= MAX_P2M_PFN || pfn_e >= MAX_P2M_PFN))
+                return 0;
+        if (unlikely(xen_feature(XENFEAT_auto_translated_physmap)))
+                return pfn_e - pfn_s;
+        if (pfn_s > pfn_e)
+                return 0;
+        for (pfn = (pfn_s & ~(P2M_MID_PER_PAGE * P2M_PER_PAGE - 1));
+                pfn < ALIGN(pfn_e, (P2M_MID_PER_PAGE * P2M_PER_PAGE));
+                pfn += P2M_MID_PER_PAGE * P2M_PER_PAGE)
+        {
+                unsigned topidx = p2m_top_index(pfn);
+                if (p2m_top[topidx] == p2m_mid_missing) {
+                        unsigned long **mid = extend_brk(PAGE_SIZE, PAGE_SIZE);
+                        p2m_mid_init(mid);
+                        p2m_top[topidx] = mid;
+                }
+        }
+        __early_alloc_p2m(pfn_s);
+        __early_alloc_p2m(pfn_e);
+        for (pfn = pfn_s; pfn < pfn_e; pfn++)
+                if (!__set_phys_to_machine(pfn, IDENTITY_FRAME(pfn)))
+                        break;
+        if (!WARN((pfn - pfn_s) != (pfn_e - pfn_s),
+                "Identity mapping failed. We are %ld short of 1-1 mappings!\n",
+                (pfn_e - pfn_s) - (pfn - pfn_s)))
+                printk(KERN_DEBUG "1-1 mapping on %lx->%lx\n", pfn_s, pfn);
+        return pfn - pfn_s;
+}
 /* Try to install p2m mapping; fail if intermediate bits missing */
 bool __set_phys_to_machine(unsigned long pfn, unsigned long mfn)
 {
        unsigned topidx, mididx, idx;
+        if (unlikely(xen_feature(XENFEAT_auto_translated_physmap))) {
+                BUG_ON(pfn != mfn && mfn != INVALID_P2M_ENTRY);
+                return true;
+        }
        if (unlikely(pfn >= MAX_P2M_PFN)) {
                BUG_ON(mfn != INVALID_P2M_ENTRY);
                return true;
@@ -368,6 +591,21 @@ bool __set_phys_to_machine(unsigned long pfn, unsigned long mfn)
        mididx = p2m_mid_index(pfn);
        idx = p2m_index(pfn);
+        /* For sparse holes were the p2m leaf has real PFN along with
+         * PCI holes, stick in the PFN as the MFN value.
+         */
+        if (mfn != INVALID_P2M_ENTRY && (mfn & IDENTITY_FRAME_BIT)) {
+                if (p2m_top[topidx][mididx] == p2m_identity)
+                        return true;
+                /* Swap over from MISSING to IDENTITY if needed. */
+                if (p2m_top[topidx][mididx] == p2m_missing) {
+                        WARN_ON(cmpxchg(&p2m_top[topidx][mididx], p2m_missing,
+                                p2m_identity) != p2m_missing);
+                        return true;
+                }
+        }
        if (p2m_top[topidx][mididx] == p2m_missing)
                return mfn == INVALID_P2M_ENTRY;
@@ -378,11 +616,6 @@ bool __set_phys_to_machine(unsigned long pfn, unsigned long mfn)
 bool set_phys_to_machine(unsigned long pfn, unsigned long mfn)
 {
-        if (unlikely(xen_feature(XENFEAT_auto_translated_physmap))) {
-                BUG_ON(pfn != mfn && mfn != INVALID_P2M_ENTRY);
-                return true;
-        }
        if (unlikely(!__set_phys_to_machine(pfn, mfn)))  {
                if (!alloc_p2m(pfn))
                        return false;
@@ -520,3 +753,80 @@ unsigned long m2p_find_override_pfn(unsigned long mfn, unsigned long pfn)
        return ret;
 }
 EXPORT_SYMBOL_GPL(m2p_find_override_pfn);
+#ifdef CONFIG_XEN_DEBUG_FS
+int p2m_dump_show(struct seq_file *m, void *v)
+{
+        static const char * const level_name[] = { "top", "middle",
+                                                "entry", "abnormal" };
+        static const char * const type_name[] = { "identity", "missing",
+                                                "pfn", "abnormal"};
+#define TYPE_IDENTITY 0
+#define TYPE_MISSING 1
+#define TYPE_PFN 2
+#define TYPE_UNKNOWN 3
+        unsigned long pfn, prev_pfn_type = 0, prev_pfn_level = 0;
+        unsigned int uninitialized_var(prev_level);
+        unsigned int uninitialized_var(prev_type);
+        if (!p2m_top)
+                return 0;
+        for (pfn = 0; pfn < MAX_DOMAIN_PAGES; pfn++) {
+                unsigned topidx = p2m_top_index(pfn);
+                unsigned mididx = p2m_mid_index(pfn);
+                unsigned idx = p2m_index(pfn);
+                unsigned lvl, type;
+                lvl = 4;
+                type = TYPE_UNKNOWN;
+                if (p2m_top[topidx] == p2m_mid_missing) {
+                        lvl = 0; type = TYPE_MISSING;
+                } else if (p2m_top[topidx] == NULL) {
+                        lvl = 0; type = TYPE_UNKNOWN;
+                } else if (p2m_top[topidx][mididx] == NULL) {
+                        lvl = 1; type = TYPE_UNKNOWN;
+                } else if (p2m_top[topidx][mididx] == p2m_identity) {
+                        lvl = 1; type = TYPE_IDENTITY;
+                } else if (p2m_top[topidx][mididx] == p2m_missing) {
+                        lvl = 1; type = TYPE_MISSING;
+                } else if (p2m_top[topidx][mididx][idx] == 0) {
+                        lvl = 2; type = TYPE_UNKNOWN;
+                } else if (p2m_top[topidx][mididx][idx] == IDENTITY_FRAME(pfn)) {
+                        lvl = 2; type = TYPE_IDENTITY;
+                } else if (p2m_top[topidx][mididx][idx] == INVALID_P2M_ENTRY) {
+                        lvl = 2; type = TYPE_MISSING;
+                } else if (p2m_top[topidx][mididx][idx] == pfn) {
+                        lvl = 2; type = TYPE_PFN;
+                } else if (p2m_top[topidx][mididx][idx] != pfn) {
+                        lvl = 2; type = TYPE_PFN;
+                }
+                if (pfn == 0) {
+                        prev_level = lvl;
+                        prev_type = type;
+                }
+                if (pfn == MAX_DOMAIN_PAGES-1) {
+                        lvl = 3;
+                        type = TYPE_UNKNOWN;
+                }
+                if (prev_type != type) {
+                        seq_printf(m, " [0x%lx->0x%lx] %s\n",
+                                prev_pfn_type, pfn, type_name[prev_type]);
+                        prev_pfn_type = pfn;
+                        prev_type = type;
+                }
+                if (prev_level != lvl) {
+                        seq_printf(m, " [0x%lx->0x%lx] level %s\n",
+                                prev_pfn_level, pfn, level_name[prev_level]);
+                        prev_pfn_level = pfn;
+                        prev_level = lvl;
+                }
+        }
+        return 0;
+#undef TYPE_IDENTITY
+#undef TYPE_MISSING
+#undef TYPE_PFN
+#undef TYPE_UNKNOWN
+}
+#endif
diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index a8a66a50d446..fa0269a99377 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -52,6 +52,8 @@ phys_addr_t xen_extra_mem_start, xen_extra_mem_size;
 static __init void xen_add_extra_mem(unsigned long pages)
 {
+        unsigned long pfn;
        u64 size = (u64)pages * PAGE_SIZE;
        u64 extra_start = xen_extra_mem_start + xen_extra_mem_size;
@@ -66,6 +68,9 @@ static __init void xen_add_extra_mem(unsigned long pages)
        xen_extra_mem_size += size;
        xen_max_p2m_pfn = PFN_DOWN(extra_start + size);
+        for (pfn = PFN_DOWN(extra_start); pfn <= xen_max_p2m_pfn; pfn++)
+                __set_phys_to_machine(pfn, INVALID_P2M_ENTRY);
 }
 static unsigned long __init xen_release_chunk(phys_addr_t start_addr,
@@ -104,7 +109,7 @@ static unsigned long __init xen_release_chunk(phys_addr_t start_addr,
                WARN(ret != 1, "Failed to release memory %lx-%lx err=%d\n",
                     start, end, ret);
                if (ret == 1) {
-                        set_phys_to_machine(pfn, INVALID_P2M_ENTRY);
+                        __set_phys_to_machine(pfn, INVALID_P2M_ENTRY);
                        len++;
                }
        }
@@ -138,12 +143,55 @@ static unsigned long __init xen_return_unused_memory(unsigned long max_pfn,
        return released;
 }
+static unsigned long __init xen_set_identity(const struct e820entry *list,
+                                             ssize_t map_size)
+{
+        phys_addr_t last = xen_initial_domain() ? 0 : ISA_END_ADDRESS;
+        phys_addr_t start_pci = last;
+        const struct e820entry *entry;
+        unsigned long identity = 0;
+        int i;
+        for (i = 0, entry = list; i < map_size; i++, entry++) {
+                phys_addr_t start = entry->addr;
+                phys_addr_t end = start + entry->size;
+                if (start < last)
+                        start = last;
+                if (end <= start)
+                        continue;
+                /* Skip over the 1MB region. */
+                if (last > end)
+                        continue;
+                if (entry->type == E820_RAM) {
+                        if (start > start_pci)
+                                identity += set_phys_range_identity(
+                                                PFN_UP(start_pci), PFN_DOWN(start));
+                        /* Without saving 'last' we would gooble RAM too
+                         * at the end of the loop. */
+                        last = end;
+                        start_pci = end;
+                        continue;
+                }
+                start_pci = min(start, start_pci);
+                last = end;
+        }
+        if (last > start_pci)
+                identity += set_phys_range_identity(
+                                        PFN_UP(start_pci), PFN_DOWN(last));
+        return identity;
+}
 /**
 * machine_specific_memory_setup - Hook for machine specific memory setup.
 **/
 char * __init xen_memory_setup(void)
 {
        static struct e820entry map[E820MAX] __initdata;
+        static struct e820entry map_raw[E820MAX] __initdata;
        unsigned long max_pfn = xen_start_info->nr_pages;
        unsigned long long mem_end;
@@ -151,6 +199,7 @@ char * __init xen_memory_setup(void)
        struct xen_memory_map memmap;
        unsigned long extra_pages = 0;
        unsigned long extra_limit;
+        unsigned long identity_pages = 0;
        int i;
        int op;
@@ -176,6 +225,7 @@ char * __init xen_memory_setup(void)
        }
        BUG_ON(rc);
+        memcpy(map_raw, map, sizeof(map));
        e820.nr_map = 0;
        xen_extra_mem_start = mem_end;
        for (i = 0; i < memmap.nr_entries; i++) {
@@ -194,6 +244,15 @@ char * __init xen_memory_setup(void)
                        end -= delta;
                        extra_pages += PFN_DOWN(delta);
+                        /*
+                         * Set RAM below 4GB that is not for us to be unusable.
+                         * This prevents "System RAM" address space from being
+                         * used as potential resource for I/O address (happens
+                         * when 'allocate_resource' is called).
+                         */
+                        if (delta &&
+                                (xen_initial_domain() && end < 0x100000000ULL))
+                                e820_add_region(end, delta, E820_UNUSABLE);
                }
                if (map[i].size > 0 && end > xen_extra_mem_start)
@@ -251,6 +310,13 @@ char * __init xen_memory_setup(void)
        xen_add_extra_mem(extra_pages);
+        /*
+         * Set P2M for all non-RAM pages and E820 gaps to be identity
+         * type PFNs. We supply it with the non-sanitized version
+         * of the E820.
+         */
+        identity_pages = xen_set_identity(map_raw, memmap.nr_entries);
+        printk(KERN_INFO "Set %ld page(s) to 1-1 mapping.\n", identity_pages);
        return "Xen";
 }
diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
index 43f9f02c7db0..b1661cd416b0 100644
--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -296,7 +296,7 @@ static int decrease_reservation(unsigned long nr_pages)
        /* No more mappings: invalidate P2M and add to balloon. */
        for (i = 0; i < nr_pages; i++) {
                pfn = mfn_to_pfn(frame_list[i]);
-                set_phys_to_machine(pfn, INVALID_P2M_ENTRY);
+                __set_phys_to_machine(pfn, INVALID_P2M_ENTRY);
                balloon_append(pfn_to_page(pfn));
        }