The branch main has been updated by kib: URL: https://cgit.FreeBSD.org/src/commit/?id=963a92d63b7443d27588fb4260bd4226f7525117
commit 963a92d63b7443d27588fb4260bd4226f7525117 Author: Konstantin Belousov <[email protected]> AuthorDate: 2026-05-31 19:15:37 +0000 Commit: Konstantin Belousov <[email protected]> CommitDate: 2026-05-31 19:18:46 +0000 amd64: explain in more details why the slop is needed Sponsored by: The FreeBSD Foundation MFC after: 1 week --- stand/man/loader.efi.8 | 3 +++ sys/amd64/amd64/machdep.c | 7 +++++++ 2 files changed, 10 insertions(+) diff --git a/stand/man/loader.efi.8 b/stand/man/loader.efi.8 index 32729ff519a2..d9ee55ee192e 100644 --- a/stand/man/loader.efi.8 +++ b/stand/man/loader.efi.8 @@ -261,7 +261,10 @@ Invalid syntax and the like are silently ignored. .Ss Staging Slop The kernel must parse the firmware memory map tables to know what memory it can use. +It also needs to allocate memory for the kernel page tables. Since it must allocate memory to do this, +without overwriting important structures, +for instance the trampoline page table, .Nm ensures there's extra memory available, called .Dq slop , diff --git a/sys/amd64/amd64/machdep.c b/sys/amd64/amd64/machdep.c index 8df4868f5312..79bef08f8a64 100644 --- a/sys/amd64/amd64/machdep.c +++ b/sys/amd64/amd64/machdep.c @@ -1273,6 +1273,13 @@ amd64_bsp_ist_init(struct pcpu *pc) * - there is a usable memory block right after the end of the * mapped kernel and all modules/metadata, pointed to by * physfree, for early allocations + * + * The memory block after the end of the kernel is important, loader + * must ensure that no critical data structures are put there. Among + * them is the trampoline page table, which must not be overwritten by + * the allocations until pmap_bootstrap() switches %cr3 to the initial + * version of the kernel page table. Size of the block is controlled + * by the 'staging_slop' command for loader.efi. */ vm_paddr_t __nosanitizeaddress __nosanitizememory amd64_loadaddr(void)
