2 files changed, 240 insertions, 4 deletions

diff --git a/arch/x86/include/asm/xen/page.h b/arch/x86/include/asm/xen/page.h
index 8ea977277c55..65fa4f26aa34 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                                                \
@@ -42,6 +44,8 @@ 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);
@@ -58,7 +62,7 @@ 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;
 }
diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
index df4e36775339..809fe3536301 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>
@@ -59,9 +182,15 @@ 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 +350,9 @@ 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
@@ -272,6 +404,14 @@ 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);
@@ -341,9 +481,11 @@ 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)
@@ -351,7 +493,7 @@ 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);
@@ -360,6 +502,82 @@ 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)
 {
@@ -378,6 +596,20 @@ 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) {
+                        p2m_top[topidx][mididx] = p2m_identity;
+                        return true;
+                }
+        }
+
         if (p2m_top[topidx][mididx] == p2m_missing)
                 return mfn == INVALID_P2M_ENTRY;