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Move the creation of linear-memory guard pages into the mmap module.

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Create linear-memory pages as PROT_NONE and then make them accessible on
demand.
This commit is contained in:
Dan Gohman
2019-01-05 16:19:50 -08:00
parent 3ac4269dc5
commit 3143e22566
2 changed files with 183 additions and 71 deletions
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40
lib/runtime/src/memory.rs
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@@ -4,7 +4,6 @@
use crate::mmap::Mmap;
use crate::vmcontext::VMMemoryDefinition;
use region;
use std::string::String;
use wasmtime_environ::{MemoryPlan, MemoryStyle, WASM_MAX_PAGES, WASM_PAGE_SIZE};
@@ -58,23 +57,8 @@ impl LinearMemory {
let request_bytes = minimum_bytes.checked_add(offset_guard_bytes).unwrap();
let mapped_pages = plan.memory.minimum as usize;
let mapped_bytes = mapped_pages * WASM_PAGE_SIZE as usize;
let unmapped_pages = minimum_pages - mapped_pages;
let unmapped_bytes = unmapped_pages * WASM_PAGE_SIZE as usize;
let inaccessible_bytes = unmapped_bytes + offset_guard_bytes;
let mmap = Mmap::with_size(request_bytes)?;
// Make the unmapped and offset-guard pages inaccessible.
if request_bytes != 0 {
unsafe {
region::protect(
mmap.as_ptr().add(mapped_bytes),
inaccessible_bytes,
region::Protection::None,
)
}
.expect("unable to make memory inaccessible");
}
let mmap = Mmap::accessible_reserved(mapped_bytes, request_bytes)?;
Ok(Self {
mmap,
@@ -117,29 +101,25 @@ impl LinearMemory {
return None;
}
let new_bytes = new_pages as usize * WASM_PAGE_SIZE as usize;
let delta_bytes = cast::usize(delta) * WASM_PAGE_SIZE as usize;
let prev_bytes = cast::usize(prev_pages) * WASM_PAGE_SIZE as usize;
let new_bytes = cast::usize(new_pages) * WASM_PAGE_SIZE as usize;
if new_bytes > self.mmap.len() - self.offset_guard_size {
// If we have no maximum, this is a "dynamic" heap, and it's allowed to move.
// If the new size is within the declared maximum, but needs more memory than we
// have on hand, it's a dynamic heap and it can move.
let guard_bytes = self.offset_guard_size;
let request_bytes = new_bytes.checked_add(guard_bytes)?;
let mut new_mmap = Mmap::with_size(request_bytes).ok()?;
// Make the offset-guard pages inaccessible.
unsafe {
region::protect(
new_mmap.as_ptr().add(new_bytes),
guard_bytes,
region::Protection::None,
)
}
.expect("unable to make memory inaccessible");
let mut new_mmap = Mmap::accessible_reserved(new_bytes, request_bytes).ok()?;
let copy_len = self.mmap.len() - self.offset_guard_size;
new_mmap.as_mut_slice()[..copy_len].copy_from_slice(&self.mmap.as_slice()[..copy_len]);
self.mmap = new_mmap;
} else {
// Make the newly allocated pages accessible.
self.mmap.make_accessible(prev_bytes, delta_bytes).ok()?;
}
self.current = new_pages;