mpu: Return largest possible order from failed v_lookup

v_lookup() is used during unmap() and as such needs to return the largest possible order for addresses that are not mapped in any region. Otherwise unmap() iterates the address space in 2M steps, which takes essentially forever. Co-authored-by: Jan Klötzke <[email protected]> Change-Id: I8891b68b1791685a9c3598edbeec4fb615741591
kernkonzept · Aug 14, 2024 · a179530 · a179530
1 parent 4836983
commit a179530
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Showing 2 changed files with 32 additions and 6 deletions.
diff --git a/src/kern/arm/mem_space-arm.cpp b/src/kern/arm/mem_space-arm.cpp
@@ -427,6 +427,7 @@ IMPLEMENTATION [arm && mpu]:
 #include <cassert>
 #include <cstring>
 
+#include "arithmetic.h"
 #include "atomic.h"
 #include "config.h"
 #include "kmem.h"
@@ -556,15 +557,27 @@ bool
 Mem_space::v_lookup(Vaddr virt, Phys_addr *phys,
                     Page_order *order, Attr *page_attribs)
 {
-  // MUST be reported in any case! The mapdb relies on this information.
-  if (order)
-    *order = Page_order(Config::SUPERPAGE_SHIFT);
-
   auto guard = lock_guard(_lock);
 
-  auto r = _dir->find(Vaddr::val(virt));
+  Mword v(Vaddr::val(virt));
+  auto r = _dir->find(v);
   if (!r)
-    return false;
+    {
+      if (order)
+        {
+          // Calculate the largest possible order that covers the gap to make
+          // iterating over the vast address space during unmap() viable.
+          Mword gap_end(0);
+          auto n = _dir->find_next(v);
+          if (n)
+            gap_end = n->start();
+          Mword gap_size = gap_end - v;
+          unsigned gap_order = gap_size ? cxx::log2u(gap_size) : MWORD_BITS - 1;
+          unsigned max_order = v ? __builtin_ctzl(v) : MWORD_BITS - 1;
+          *order = Page_order(min(gap_order, max_order));
+        }
+      return false;
+    }
 
   // We always need to report the smallest order. The disabled code below that
   // tries to report the order more truthfully breaks mapdb.

diff --git a/src/kern/mpu.cpp b/src/kern/mpu.cpp
@@ -515,6 +515,19 @@ Mpu_regions::find(Mword addr) const
   return nullptr;
 }
 
+PUBLIC inline
+Mpu_region const *
+Mpu_regions::find_next(Mword addr) const
+{
+  for (auto const &i : _used_list)
+    {
+      if (addr < i->start())
+        return i;
+    }
+
+  return nullptr;
+}
+
 /**
  * Dump regions list.
  */