[Xen-devel] [RFC 12/22] xen/arm: p2m: Introduce p2m_get_entry and use it to implement __p2m_lookup

[Julien Grall <julien.grall@xxxxxxx>]

Currently, for a given GFN, the function __p2m_lookup will only return
the associated MFN and the p2m type of the mapping.

In some case we need the order of the mapping and the memaccess
permission. Rather than providing separate function for this purpose,
it is better to implement a generic function to return all the
information.

To avoid passing dummy parameter, a caller that does need a specific
information can use NULL instead.

The list of the informations retrieved is based on the x86 version. All
of them will be used in follow-up patches.

It might have been possible to extend __p2m_lookup, however I choose to
reimplement it from scratch to allow sharing some helpers with the
function that will update the P2M (will be added in a follow-up patch).

Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
---
 xen/arch/arm/p2m.c         | 188 ++++++++++++++++++++++++++++++++++-----------
 xen/include/asm-arm/page.h |   4 +
 2 files changed, 149 insertions(+), 43 deletions(-)

diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
index d4a4b62..8676b9d 100644
--- a/xen/arch/arm/p2m.c
+++ b/xen/arch/arm/p2m.c
@@ -36,6 +36,8 @@ static const paddr_t level_masks[] =
     { ZEROETH_MASK, FIRST_MASK, SECOND_MASK, THIRD_MASK };
 static const unsigned int level_shifts[] =
     { ZEROETH_SHIFT, FIRST_SHIFT, SECOND_SHIFT, THIRD_SHIFT };
+static const unsigned int level_orders[] =
+    { ZEROETH_ORDER, FIRST_ORDER, SECOND_ORDER, THIRD_ORDER };
 
 static bool_t p2m_valid(lpae_t pte)
 {
@@ -236,28 +238,99 @@ static lpae_t *p2m_get_root_pointer(struct p2m_domain 
*p2m,
 
 /*
  * Lookup the MFN corresponding to a domain's GFN.
+ * Lookup mem access in the ratrix tree.
+ * The entries associated to the GFN is considered valid.
+ */
+static p2m_access_t p2m_mem_access_radix_get(struct p2m_domain *p2m, gfn_t gfn)
+{
+    void *ptr;
+
+    if ( !p2m->mem_access_enabled )
+        return p2m_access_rwx;
+
+    ptr = radix_tree_lookup(&p2m->mem_access_settings, gfn_x(gfn));
+    if ( !ptr )
+        return p2m_access_rwx;
+    else
+        return radix_tree_ptr_to_int(ptr);
+}
+
+#define GUEST_TABLE_MAP_FAILED 0
+#define GUEST_TABLE_SUPER_PAGE 1
+#define GUEST_TABLE_NORMAL_PAGE 2
+
+static int p2m_create_table(struct p2m_domain *p2m, lpae_t *entry,
+                            int level_shift);
+
+/*
+ * Take the currently mapped table, find the corresponding GFN entry,
+ * and map the next table, if available.
  *
- * There are no processor functions to do a stage 2 only lookup therefore we
- * do a a software walk.
+ * Return values:
+ *  GUEST_TABLE_MAP_FAILED: Either read_only was set and the entry
+ *  was empty, or allocating a new page failed.
+ *  GUEST_TABLE_NORMAL_PAGE: next level mapped normally
+ *  GUEST_TABLE_SUPER_PAGE: The next entry points to a superpage.
  */
-static mfn_t __p2m_lookup(struct domain *d, gfn_t gfn, p2m_type_t *t)
+static int p2m_next_level(struct p2m_domain *p2m, bool read_only,
+                          lpae_t **table, unsigned int offset)
 {
-    struct p2m_domain *p2m = &d->arch.p2m;
-    const paddr_t paddr = pfn_to_paddr(gfn_x(gfn));
-    const unsigned int offsets[4] = {
-        zeroeth_table_offset(paddr),
-        first_table_offset(paddr),
-        second_table_offset(paddr),
-        third_table_offset(paddr)
-    };
-    const paddr_t masks[4] = {
-        ZEROETH_MASK, FIRST_MASK, SECOND_MASK, THIRD_MASK
-    };
-    lpae_t pte, *map;
+    lpae_t *entry;
+    int ret;
+    mfn_t mfn;
+
+    entry = *table + offset;
+
+    if ( !p2m_valid(*entry) )
+    {
+        if ( read_only )
+            return GUEST_TABLE_MAP_FAILED;
+
+        ret = p2m_create_table(p2m, entry, /* not used */ ~0);
+        if ( ret )
+            return GUEST_TABLE_MAP_FAILED;
+    }
+
+    /* The function p2m_next_level is never called at the 3rd level */
+    if ( p2m_mapping(*entry) )
+        return GUEST_TABLE_SUPER_PAGE;
+
+    mfn = _mfn(entry->p2m.base);
+
+    unmap_domain_page(*table);
+    *table = map_domain_page(mfn);
+
+    return GUEST_TABLE_NORMAL_PAGE;
+}
+
+/*
+ * Get the details of a given gfn.
+ *
+ * If the entry is present, the associated MFN will be returned and the
+ * access and type filled up. The page_order will correspond to the
+ * order of the mapping in the page table (i.e it could be a superpage).
+ *
+ * If the entry is not present, INVALID_MFN will be returned and the
+ * page_order will be set according to the order of the invalid range.
+ */
+static mfn_t p2m_get_entry(struct p2m_domain *p2m, gfn_t gfn,
+                           p2m_type_t *t, p2m_access_t *a,
+                           unsigned int *page_order)
+{
+    paddr_t addr = pfn_to_paddr(gfn_x(gfn));
+    unsigned int level = 0;
+    lpae_t entry, *table;
+    int rc;
     mfn_t mfn = INVALID_MFN;
-    paddr_t mask = 0;
     p2m_type_t _t;
-    unsigned int level;
+
+    /* Convenience aliases */
+    const unsigned int offsets[4] = {
+        zeroeth_table_offset(addr),
+        first_table_offset(addr),
+        second_table_offset(addr),
+        third_table_offset(addr)
+    };
 
     ASSERT(p2m_is_locked(p2m));
     BUILD_BUG_ON(THIRD_MASK != PAGE_MASK);
@@ -267,46 +340,75 @@ static mfn_t __p2m_lookup(struct domain *d, gfn_t gfn, 
p2m_type_t *t)
 
     *t = p2m_invalid;
 
-    map = p2m_get_root_pointer(p2m, gfn);
-    if ( !map )
-        return INVALID_MFN;
+    /* XXX: Check if the mapping is lower than the mapped gfn */
 
-    ASSERT(P2M_ROOT_LEVEL < 4);
-
-    for ( level = P2M_ROOT_LEVEL ; level < 4 ; level++ )
+    /* This gfn is higher than the highest the p2m map currently holds */
+    if ( gfn_x(gfn) > gfn_x(p2m->max_mapped_gfn) )
     {
-        mask = masks[level];
-
-        pte = map[offsets[level]];
+        for ( level = P2M_ROOT_LEVEL; level < 3; level++ )
+        {
+            if ( (gfn_x(gfn) & (level_masks[level] >> PAGE_SHIFT)) >
+                 gfn_x(p2m->max_mapped_gfn) )
+                break;
+            goto out;
+        }
+    }
 
-        if ( level == 3 && !p2m_table(pte) )
-            /* Invalid, clobber the pte */
-            pte.bits = 0;
-        if ( level == 3 || !p2m_table(pte) )
-            /* Done */
-            break;
+    table = p2m_get_root_pointer(p2m, gfn);
 
-        ASSERT(level < 3);
+    /*
+     * the table should always be non-NULL because the gfn is below
+     * p2m->max_mapped_gfn and the root table pages are always present.
+     */
+    BUG_ON(table == NULL);
 
-        /* Map for next level */
-        unmap_domain_page(map);
-        map = map_domain_page(_mfn(pte.p2m.base));
+    for ( level = P2M_ROOT_LEVEL; level < 3; level++ )
+    {
+        rc = p2m_next_level(p2m, true, &table, offsets[level]);
+        if ( rc == GUEST_TABLE_MAP_FAILED )
+            goto out_unmap;
+        else if ( rc != GUEST_TABLE_NORMAL_PAGE )
+            break;
     }
 
-    unmap_domain_page(map);
+    entry = table[offsets[level]];
 
-    if ( p2m_valid(pte) )
+    if ( p2m_valid(entry) )
     {
-        ASSERT(mask);
-        ASSERT(pte.p2m.type != p2m_invalid);
-        mfn = _mfn(paddr_to_pfn((pte.bits & PADDR_MASK & mask) |
-                                (paddr & ~mask)));
-        *t = pte.p2m.type;
+        *t = entry.p2m.type;
+
+        if ( a )
+            *a = p2m_mem_access_radix_get(p2m, gfn);
+
+        mfn = _mfn(entry.p2m.base);
+        /*
+         * The entry may point to a superpage. Find the MFN associated
+         * to the GFN.
+         */
+        mfn = mfn_add(mfn, gfn_x(gfn) & ((1UL << level_orders[level]) - 1));
     }
 
+out_unmap:
+    unmap_domain_page(table);
+
+out:
+    if ( page_order )
+        *page_order = level_shifts[level] - PAGE_SHIFT;
+
     return mfn;
 }
 
+/*
+ * Lookup the MFN corresponding to a domain's GFN.
+ *
+ * There are no processor functions to do a stage 2 only lookup therefore we
+ * do a a software walk.
+ */
+static mfn_t __p2m_lookup(struct domain *d, gfn_t gfn, p2m_type_t *t)
+{
+    return p2m_get_entry(&d->arch.p2m, gfn, t, NULL, NULL);
+}
+
 mfn_t p2m_lookup(struct domain *d, gfn_t gfn, p2m_type_t *t)
 {
     mfn_t ret;
diff --git a/xen/include/asm-arm/page.h b/xen/include/asm-arm/page.h
index 05d9f82..1c5bd8b 100644
--- a/xen/include/asm-arm/page.h
+++ b/xen/include/asm-arm/page.h
@@ -457,15 +457,19 @@ static inline int gva_to_ipa(vaddr_t va, paddr_t *paddr, 
unsigned int flags)
 #define LPAE_ENTRY_MASK (LPAE_ENTRIES - 1)
 
 #define THIRD_SHIFT    (PAGE_SHIFT)
+#define THIRD_ORDER    0
 #define THIRD_SIZE     ((paddr_t)1 << THIRD_SHIFT)
 #define THIRD_MASK     (~(THIRD_SIZE - 1))
 #define SECOND_SHIFT   (THIRD_SHIFT + LPAE_SHIFT)
+#define SECOND_ORDER   (THIRD_ORDER + LPAE_SHIFT)
 #define SECOND_SIZE    ((paddr_t)1 << SECOND_SHIFT)
 #define SECOND_MASK    (~(SECOND_SIZE - 1))
 #define FIRST_SHIFT    (SECOND_SHIFT + LPAE_SHIFT)
+#define FIRST_ORDER    (SECOND_ORDER + LPAE_SHIFT)
 #define FIRST_SIZE     ((paddr_t)1 << FIRST_SHIFT)
 #define FIRST_MASK     (~(FIRST_SIZE - 1))
 #define ZEROETH_SHIFT  (FIRST_SHIFT + LPAE_SHIFT)
+#define ZEROETH_ORDER  (FIRST_ORDER + LPAE_SHIFT)
 #define ZEROETH_SIZE   ((paddr_t)1 << ZEROETH_SHIFT)
 #define ZEROETH_MASK   (~(ZEROETH_SIZE - 1))
 
-- 
1.9.1


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