A processor includes a cache hierarchy including a level-1 cache and a higher-level cache. The processor maps a portion of physical memory space to a portion of the higher-level cache, executes instructions, at least some of which comprise microcode, allows microcode to access the portion of the higher-level cache, and prevents instructions that do not comprise microcode from accessing the portion of the higher-level cache. The first portion of the physical memory space can be permanently allocated for use by microcode. The processor can move one or more cache lines of the first portion of the higher-level cache from the higher-level cache to a first portion of the level-1 cache, allow microcode to access the first portion of the first level-1 cache, and prevent instructions that do not comprise microcode from accessing the first portion of the first level-1 cache.