[kernel] Add TLB invalidation when unmapping pages

This has always been on the todo list, but it finally bit me. srv.init
re-uses load addresses when loading multiple programs, and collision
between reused addresses was causing corruption without the TLB flush.
Now srv.init also doesn't increment its load address for sections when
loading a single program either, since unmapping pages actually works.

src/kernel/vm_space.cpp

@@ -228,6 +228,12 @@ vm_space::clear(const obj::vm_area &vma, uintptr_t offset, size_t count, bool fr
         uintptr_t phys = e & ~0xfffull;
 
         if (e & page_table::flag::present) {
+            uint64_t orig = e;
+            e = 0;
+            if (orig & page_table::flag::accessed) {
+                auto *addr = reinterpret_cast<const uint8_t *>(it.vaddress());
+                asm ( "invlpg %0" :: "m"(*addr) : "memory" );
+            }
             if (free_count && phys == free_start + (free_count * frame_size)) {
                 ++free_count;
             } else {
@@ -238,7 +244,6 @@ vm_space::clear(const obj::vm_area &vma, uintptr_t offset, size_t count, bool fr
             }
         }
 
-        e = 0;
         ++it;
     }
 
@@ -286,12 +291,14 @@ vm_space::handle_fault(uintptr_t addr, fault_type fault)
     if (fault && fault_type::present)
         return false;
 
+    uintptr_t page = (addr & ~0xfffull);
+
     uintptr_t base = 0;
     obj::vm_area *area = get(addr, &base);
     if (!area)
         return false;
 
-    uintptr_t offset = (addr & ~0xfffull) - base;
+    uintptr_t offset = page - base;
     uintptr_t phys_page = 0;
     if (!area->get_page(offset, phys_page))
         return false;