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We allow requesting an explicit memory type when calling map_physical_memory but default to the uncached B_MTR_UC when not given. When called without an explicitly requested memory type, allow arch_vm_set_memory_type to modify and return an effective memory type. When an overlapping range already exists, the effective memory type is set to the one of the existing mapping. If there is an explicit memory type request that conflicts with an existing range, or if multiple overlaps with conflicting types would be produced, the mapping is disallow (and a panic is triggered under KDEBUG). This effectively detects and panics when conflicting aliases of physical memory would be created. This is also useful on an MTRR based setup, as such overlaps cannot be properly represented. When using the page attribute table (PAT) to set the memory type on a per page virtual memory mapping basis, this is needed to prevent aliasing of the same physical memory with different types. As per the specs, such aliasing is unsupported and may result in undefined operations that lead to system failure. The mechanism is extended to the general arch_vm_set_memory_type as such aliasing prevention also seems to apply to other architectures (at least on ARM, aliasing is also strongly discouraged). Change-Id: I7aaf6ea8415e92e74cd1643b67793a6857619eea Reviewed-on: https://review.haiku-os.org/c/haiku/+/8339 Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org> Reviewed-by: waddlesplash <waddlesplash@gmail.com>