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Limit BIOS bootloader's max_phys_addr to 4 GiB #260

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Merged
merged 2 commits into from
Sep 25, 2022
Merged

Limit BIOS bootloader's max_phys_addr to 4 GiB #260

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cd2761e
Limit BIOS bootloader's `max_phys_addr` to 4 GiB
hawkw Sep 22, 2022
4da46e1
Allow mapping part of a region if it crosses 4 GiB
hawkw Sep 22, 2022
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7 changes: 6 additions & 1 deletion src/bin/bios.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -78,6 +78,7 @@ fn bootloader_main(
use bootloader::binary::{
bios::memory_descriptor::E820MemoryRegion, legacy_memory_region::LegacyFrameAllocator,
};
const GIGABYTE: u64 = 4096 * 512 * 512;

let e820_memory_map = {
let ptr = usize_from(memory_map_addr.as_u64()) as *const E820MemoryRegion;
Expand All @@ -86,6 +87,10 @@ fn bootloader_main(
let max_phys_addr = e820_memory_map
.iter()
.map(|r| r.start_addr + r.len)
// Don't consider addresses > 4GiB when determining the maximum
// physical address for the bootloader, as we are in protected mode and
// cannot address more than 4 GiB of memory anyway.
.filter(|&addr| addr < GIGABYTE * 4)
.max()
.expect("no physical memory regions found");

Expand All @@ -106,7 +111,7 @@ fn bootloader_main(
// identity-map remaining physical memory (first gigabyte is already identity-mapped)
{
let start_frame: PhysFrame<Size2MiB> =
PhysFrame::containing_address(PhysAddr::new(4096 * 512 * 512));
PhysFrame::containing_address(PhysAddr::new(GIGABYTE));
let end_frame = PhysFrame::containing_address(PhysAddr::new(max_phys_addr - 1));
for frame in PhysFrame::range_inclusive(start_frame, end_frame) {
unsafe {
Expand Down