@@ -386,10 +386,16 @@ pub struct Mappings {
386386 pub boot_info : Mapping ,
387387 /// Specifies the mapping of the frame buffer memory region.
388388 pub framebuffer : Mapping ,
389- /// The bootloader supports to map the whole physical memory into the virtual address
389+ /// The bootloader supports mapping the whole physical memory into the virtual address
390390 /// space at some offset. This is useful for accessing and modifying the page tables set
391391 /// up by the bootloader.
392392 ///
393+ /// This mapping will go from physical address `0x0` to whichever is larger:
394+ /// - The end of the last region in the BIOS/UEFI memory map
395+ /// - The address `0x1_0000_0000` (such that at least 4 GiB of physical memory are always mapped).
396+ /// This is to ensure that useful MMIO regions (local APIC, I/O APIC, PCI bars) are
397+ /// accessible to the kernel even if less physical memory than that is on the system.
398+ ///
393399 /// Defaults to `None`, i.e. no mapping of the physical memory.
394400 pub physical_memory : Option < Mapping > ,
395401 /// As an alternative to mapping the whole physical memory (see [`Self::physical_memory`]),
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