More PR feedback changes.

* More use of `anyhow`.
* Change `make_accessible` into `protect_linear_memory` to better demonstrate
  what it is used for; this will make the uffd implementation make a little
  more sense.
* Remove `create_memory_map` in favor of just creating the `Mmap` instances in
  the pooling allocator. This also removes the need for `MAP_NORESERVE` in the
  uffd implementation.
* Moar comments.
* Remove `BasePointerIterator` in favor of `impl Iterator`.
* The uffd implementation now only monitors linear memory pages and will only
  receive faults on pages that could potentially be accessible and never on a
  statically known guard page.
* Stop allocating memory or table pools if the maximum limit of the memory or
  table is 0.

crates/wasmtime/src/trampoline/memory.rs

@@ -3,7 +3,7 @@ use crate::memory::{LinearMemory, MemoryCreator};
 use crate::trampoline::StoreInstanceHandle;
 use crate::Store;
 use crate::{Limits, MemoryType};
-use anyhow::Result;
+use anyhow::{anyhow, Result};
 use wasmtime_environ::entity::PrimaryMap;
 use wasmtime_environ::{wasm, MemoryPlan, MemoryStyle, Module, WASM_PAGE_SIZE};
 use wasmtime_runtime::{RuntimeLinearMemory, RuntimeMemoryCreator, VMMemoryDefinition};
@@ -57,7 +57,7 @@ impl RuntimeLinearMemory for LinearMemoryProxy {
 pub(crate) struct MemoryCreatorProxy(pub Arc<dyn MemoryCreator>);
 
 impl RuntimeMemoryCreator for MemoryCreatorProxy {
-    fn new_memory(&self, plan: &MemoryPlan) -> Result<Box<dyn RuntimeLinearMemory>, String> {
+    fn new_memory(&self, plan: &MemoryPlan) -> Result<Box<dyn RuntimeLinearMemory>> {
         let ty = MemoryType::new(Limits::new(plan.memory.minimum, plan.memory.maximum));
         let reserved_size_in_bytes = match plan.style {
             MemoryStyle::Static { bound } => Some(bound as u64 * WASM_PAGE_SIZE as u64),
@@ -66,5 +66,6 @@ impl RuntimeMemoryCreator for MemoryCreatorProxy {
         self.0
             .new_memory(ty, reserved_size_in_bytes, plan.offset_guard_size)
             .map(|mem| Box::new(LinearMemoryProxy { mem }) as Box<dyn RuntimeLinearMemory>)
+            .map_err(|e| anyhow!(e))
     }
 }