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fix(physicalmem): don't claim low addresses #2453

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Merged
mkroening merged 1 commit into from
Aug 18, 2026
Merged

fix(physicalmem): don't claim low addresses #2453

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13 changes: 9 additions & 4 deletions src/mm/physicalmem.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -9,7 +9,7 @@ use memory_addresses::VirtAddr;

#[cfg(all(target_arch = "x86_64", feature = "hermit-entry"))]
use crate::arch::mm::paging::PageTableEntryFlagsExt;
use crate::arch::mm::paging::{self, HugePageSize, PageSize};
use crate::arch::mm::paging::{self, HugePageSize, LargePageSize, PageSize};
use crate::env::{self, MemmapType, StartInfo};
use crate::mm::device_alloc::DeviceAlloc;
use crate::mm::{PageRangeAllocator, PageRangeBox};
Expand Down Expand Up @@ -76,7 +76,7 @@ pub unsafe fn map_frame_range(frame_range: PageRange) {
type IdentityPageSize = HugePageSize;
}
target_arch = "x86_64" => {
type IdentityPageSize = paging::LargePageSize;
type IdentityPageSize = LargePageSize;
}
}

Expand Down Expand Up @@ -118,8 +118,13 @@ unsafe fn detect_from_start_info() {
let mut start_addr = memmap_entry.phys_addr;
let mut end_addr = start_addr + memmap_entry.len;

// Don't use the zero page.
start_addr = start_addr.max(0x1000);
// Do not free any address in the real mode addressable range.
//
// When claiming physical memory, ignore all addresses below this one. This ensures we
// don't accidentally clash with hardcoded low addresses, such as `SMP_BOOT_CODE_ADDRESS`
// in x86_64 with SMP enabled. We use a 2MIB size for now, but this is arbitrary, and could
// likely be lowered.
start_addr = start_addr.max(LargePageSize::SIZE as usize);

#[cfg(all(target_arch = "x86_64", feature = "hermit-entry"))]
if paging::is_recursive() {
Expand Down
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