A couple things here, we were never returning the last searched element,
either the last or first depending on search direction.
Also the backward scan would return incorrect indexes in some cases.
Also scanning beyond its page bounds.
Additionally some minorly incorrect assertions.
Adds a new unit test that ensures that we can allocate in to every
location, and that we get the correct indexes back. Also allocated
within guarded pages to ensure it doesn't read outside the bounds.
Fixes a spurious crash in Ender Magnolia.
When small regions were being used for VMA allocations (less than 64
pages), this function was truncating the result to zero. Resulting in
incorrect `LiveVMARegion` size calculations. It would calculate that the
FlexBitSet consumes zero bits of space, even though it needs to use at
least 2, or 3 if we actually want to allocate anything from that
LiveVMARegion.
This was noticed in this PR because our VMA region tracking is being
used more, which has a more likely chance to have small VMA regions for
allocating from. Cause a 1page allocation to try and use a 3 page VMA
region for allocation, but failing because the FlexBitSet size wasn't
calculated correctly.
- Page layout:
- [0x0, 0x1000): struct LiveVMARegion
- [0x1000, 0x2000): FlexBitSet<uint64_t> UsedPages
- ^ This space wasn't allocated/mprotected due to the size not
calculating correctly.
- [0x2000, 0x3000): Memory for allocation
It is not an external component, and it makes paths needlessly long.
Ryan seemed amenable to this when we discussed on IRC earlier.
Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Ryan Houdek