fix(mmio): don't return MMIO virtual addresses to the free list (use-after-free)

[edef1c]

In check_linux_args, we return VAs to the free list while a VolatileRef to them is active. This breaks multi-device configurations. A similar bug exists in guess_device, but the current version of this patch doesn't fix it, since my reference target supplies mmio args.

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Benchmark Results

Details

Benchmark	Current: cb881f1	Previous: 4912505	Performance Ratio
startup_benchmark Build Time	99.27 s	99.11 s	1.00 ❗
startup_benchmark File Size	0.86 MB	0.86 MB	1.00 ❗
Startup Time - 1 core	0.97 s (±0.02 s)	0.96 s (±0.03 s)	1.01
Startup Time - 2 cores	0.97 s (±0.03 s)	0.96 s (±0.03 s)	1.00
Startup Time - 4 cores	0.97 s (±0.03 s)	0.96 s (±0.02 s)	1.01
multithreaded_benchmark Build Time	101.80 s	102.01 s	1.00 ❗
multithreaded_benchmark File Size	0.95 MB	0.95 MB	1.00 ❗
Multithreaded Pi Efficiency - 2 Threads	91.12 % (±6.64 %)	85.65 % (±8.90 %)	1.06
Multithreaded Pi Efficiency - 4 Threads	45.02 % (±2.75 %)	43.12 % (±3.13 %)	1.04
Multithreaded Pi Efficiency - 8 Threads	26.44 % (±1.80 %)	25.03 % (±1.95 %)	1.06
micro_benchmarks Build Time	112.93 s	114.00 s	0.99 ❗
micro_benchmarks File Size	0.96 MB	0.96 MB	1.00 ❗
Scheduling time - 1 thread	69.86 ticks (±3.84 ticks)	70.19 ticks (±3.58 ticks)	1.00
Scheduling time - 2 threads	38.47 ticks (±4.79 ticks)	38.99 ticks (±4.43 ticks)	0.99
Micro - Time for syscall (getpid)	2.94 ticks (±0.26 ticks)	2.96 ticks (±0.24 ticks)	0.99
Memcpy speed - (built_in) block size 4096	63522.17 MByte/s (±45339.86 MByte/s)	64026.03 MByte/s (±45553.92 MByte/s)	0.99
Memcpy speed - (built_in) block size 1048576	29963.60 MByte/s (±24956.52 MByte/s)	29743.12 MByte/s (±24826.10 MByte/s)	1.01
Memcpy speed - (built_in) block size 16777216	25666.85 MByte/s (±21512.30 MByte/s)	24007.89 MByte/s (±20230.77 MByte/s)	1.07
Memset speed - (built_in) block size 4096	63985.25 MByte/s (±45622.98 MByte/s)	64637.10 MByte/s (±45951.78 MByte/s)	0.99
Memset speed - (built_in) block size 1048576	30754.88 MByte/s (±25394.92 MByte/s)	30516.60 MByte/s (±25260.76 MByte/s)	1.01
Memset speed - (built_in) block size 16777216	26362.96 MByte/s (±21919.69 MByte/s)	24779.16 MByte/s (±20739.68 MByte/s)	1.06
Memcpy speed - (rust) block size 4096	58330.20 MByte/s (±43048.88 MByte/s)	60077.78 MByte/s (±44331.51 MByte/s)	0.97
Memcpy speed - (rust) block size 1048576	29827.70 MByte/s (±24862.50 MByte/s)	29870.69 MByte/s (±24878.06 MByte/s)	1.00
Memcpy speed - (rust) block size 16777216	24954.47 MByte/s (±21049.51 MByte/s)	24212.89 MByte/s (±20297.89 MByte/s)	1.03
Memset speed - (rust) block size 4096	59114.01 MByte/s (±43499.71 MByte/s)	60925.02 MByte/s (±44834.41 MByte/s)	0.97
Memset speed - (rust) block size 1048576	30628.95 MByte/s (±25305.17 MByte/s)	30651.78 MByte/s (±25309.43 MByte/s)	1.00
Memset speed - (rust) block size 16777216	25729.58 MByte/s (±21546.95 MByte/s)	24986.00 MByte/s (±20809.17 MByte/s)	1.03
alloc_benchmarks Build Time	104.48 s	105.28 s	0.99 ❗
alloc_benchmarks File Size	0.93 MB	0.93 MB	1.00 ❗
Allocations - Allocation success	100.00 %	100.00 %	1
Allocations - Deallocation success	100.00 %	100.00 %	1
Allocations - Pre-fail Allocations	100.00 %	100.00 %	1
Allocations - Average Allocation time	12659.28 Ticks (±165.88 Ticks)	9727.01 Ticks (±267.20 Ticks)	1.30 ❗
Allocations - Average Allocation time (no fail)	12659.28 Ticks (±165.88 Ticks)	9727.01 Ticks (±267.20 Ticks)	1.30 ❗
Allocations - Average Deallocation time	1065.63 Ticks (±771.58 Ticks)	2219.93 Ticks (±959.95 Ticks)	0.48
mutex_benchmark Build Time	103.58 s	104.33 s	0.99 ❗
mutex_benchmark File Size	0.96 MB	0.96 MB	1.00 ❗
Mutex Stress Test Average Time per Iteration - 1 Threads	12.92 ns (±0.66 ns)	12.84 ns (±0.76 ns)	1.01
Mutex Stress Test Average Time per Iteration - 2 Threads	15.66 ns (±0.76 ns)	15.44 ns (±0.78 ns)	1.01

This comment was automatically generated by workflow using github-action-benchmark.

[edef1c]

FWIW, it is not totally clear to me why PageBox merely reserves the VA, and leaks the mapping / doesn't unmap on Drop; the VA use-after-free would have been dead obvious in all cases with a more RAII-style design.