SP: add ArenaMap

The ArenaMap will store our internal provenance roots. This commit simply introduces the data structure and does not wire it up to the rest of the tree.
2021-01-11 12:48:49 +00:00
parent d9822036b2
commit a9722667ab
1 changed files with 130 additions and 0 deletions
--- a/src/mem/arenamap.h
+++ b/src/mem/arenamap.h
@@ -0,0 +1,130 @@
+#include "../ds/ptrwrap.h"
+#include "pagemap.h"
+
+namespace snmalloc
+{
+  struct default_alloc_size_t
+  {
+    /*
+     * Just make something up for non-StrictProvenance architectures.
+     * Ultimately, this is going to flow only to FlatPagemap's template argument
+     * for the number of bits it's covering but the whole thing will be
+     * discarded by the time we resolve all the conditionals behind the
+     * AuthPagemap type.  To avoid pathologies where COVERED_BITS ends up being
+     * bit-width of the machine (meaning 1ULL << COVERED_BITS becomes undefined)
+     * and where sizeof(std::atomic<T>[ENTRIES]) is either undefined or
+     * enormous, we choose a value that dodges both endpoints and still results
+     * in a small table.
+     */
+    static constexpr size_t capptr_root_alloc_size =
+      bits::one_at_bit(bits::ADDRESS_BITS - 8);
+  };
+
+  /*
+   * Compute the block allocation size to use for AlignedAllocations.  This
+   * is either PAL::capptr_root_alloc_size, on architectures that require
+   * StrictProvenance, or the placeholder from above.
+   */
+  template<typename PAL>
+  static constexpr size_t AUTHMAP_ALLOC_SIZE = std::conditional_t<
+    aal_supports<StrictProvenance>,
+    PAL,
+    default_alloc_size_t>::capptr_root_alloc_size;
+
+  template<typename PAL>
+  static constexpr size_t
+    AUTHMAP_BITS = bits::next_pow2_bits_const(AUTHMAP_ALLOC_SIZE<PAL>);
+
+  template<typename PAL>
+  static constexpr bool
+    AUTHMAP_USE_FLATPAGEMAP = pal_supports<LazyCommit, PAL> ||
+    (PAGEMAP_NODE_SIZE >= sizeof(FlatPagemap<AUTHMAP_BITS<PAL>, void*>));
+
+  struct default_auth_pagemap
+  {
+    static SNMALLOC_FAST_PATH void* get(address_t a)
+    {
+      UNUSED(a);
+      return nullptr;
+    }
+  };
+
+  template<typename PAL, typename PrimAlloc>
+  using AuthPagemap = std::conditional_t<
+    aal_supports<StrictProvenance>,
+    std::conditional_t<
+      AUTHMAP_USE_FLATPAGEMAP<PAL>,
+      FlatPagemap<AUTHMAP_BITS<PAL>, void*>,
+      Pagemap<AUTHMAP_BITS<PAL>, void*, nullptr, PrimAlloc>>,
+    default_auth_pagemap>;
+
+  struct ForAuthmap
+  {};
+  template<typename PAL, typename PrimAlloc>
+  using GlobalAuthmap =
+    GlobalPagemapTemplate<AuthPagemap<PAL, PrimAlloc>, ForAuthmap>;
+
+  template<SNMALLOC_CONCEPT(ConceptPAL) PAL, typename PagemapProvider>
+  struct DefaultArenaMapTemplate
+  {
+    /*
+     * Without AlignedAllocation, we (below) adopt a fallback mechanism that
+     * over-allocates and then finds an aligned region within the too-large
+     * region.  The "trimmings" from either side are also registered in hopes
+     * that they can be used for later allocations.
+     *
+     * Unfortunately, that strategy does not work for this ArenaMap: trimmings
+     * may be smaller than the granularity of our backing PageMap, and so we
+     * would be unable to amplify authority.  Eventually we may arrive at a need
+     * for an ArenaMap that is compatible with this approach, but for the moment
+     * it's far simpler to assume that we can always ask for memory sufficiently
+     * aligned to cover an entire PageMap granule.
+     */
+    static_assert(
+      !aal_supports<StrictProvenance> || pal_supports<AlignedAllocation, PAL>,
+      "StrictProvenance requires platform support for aligned allocation");
+
+    static constexpr size_t alloc_size = AUTHMAP_ALLOC_SIZE<PAL>;
+
+    /*
+     * Because we assume that we can `capptr_amplify` and then
+     * `Superslab::get()` on the result to get to the Superslab metadata
+     * headers, it must be the case that provenance roots cover entire
+     * Superslabs.
+     */
+    static_assert(
+      !aal_supports<StrictProvenance> ||
+        ((alloc_size > 0) && (alloc_size % SUPERSLAB_SIZE == 0)),
+      "Provenance root granule must encompass whole superslabs");
+
+    static void register_root(CapPtr<void, CBArena> root)
+    {
+      if constexpr (aal_supports<StrictProvenance>)
+      {
+        PagemapProvider::pagemap().set(address_cast(root), root.unsafe_capptr);
+      }
+      else
+      {
+        UNUSED(root);
+      }
+    }
+
+    template<typename T = void, typename U, capptr_bounds B>
+    static SNMALLOC_FAST_PATH CapPtr<T, CBArena> capptr_amplify(CapPtr<U, B> r)
+    {
+      static_assert(
+        B == CBAllocE || B == CBAlloc,
+        "Attempting to amplify an unexpectedly high pointer");
+      return Aal::capptr_rebound(
+               CapPtr<void, CBArena>(
+                 PagemapProvider::pagemap().get(address_cast(r))),
+               r)
+        .template as_static<T>();
+    }
+  };
+
+  template<typename PAL, typename PrimAlloc>
+  using DefaultArenaMap =
+    DefaultArenaMapTemplate<PAL, GlobalAuthmap<PAL, PrimAlloc>>;
+
+} // namespace snmalloc