Document physical memory mapping size #506
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Freax13
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Jun 5, 2025
Co-authored-by: Tom Dohrmann <Erbse.13@gmx.de>
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In developing an AHCI driver, I noticed that the addresses that UEFI loads the MMIO structures into were higher than the final memory region given by the memory map. Since I was using that final region to determine the size of the bootloader-provided physical memory map, I didn't know how far the map "truly" extended.
Digging into the source code (
common/src/legacy_memory_region.rs:141) I noticed that the bootloader continues mapping up to 4 GiB, even if less than that is on the system (I had QEMU set to 2). Since this didn't (seem to be) documented, I added a note to the rustdoc on the physical map settings explaining this. I took some of the wording from a comment on the relevant source code. Also, fixed a typo on the same rustdoc.