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commit c208439cdb588d91aead9403cec3d4acf4a8bebf
Author: Andrew Turner <andrew@FreeBSD.org>
AuthorDate: 2026-04-13 11:50:32 +0000
Commit: Andrew Turner <andrew@FreeBSD.org>
CommitDate: 2026-04-13 14:23:05 +0000
arm64: Add a cmap page to pmap
When modifying mappings in pmap we may need to perform a
break-before-make sequence. This creates an invalid mapping, then
recreates it with the changes.
When modifying DMAP mappings we may be changing the mapping that
contains its own page table then after breaking the old entry we are
unable to create the new entry.
To fix this create a map that can be used & won't be affected by the
break-before-make sequence.
Reviewed by: kib
Sponsored by: Arm Ltd
Differential Revision: https://reviews.freebsd.org/D56306
---
sys/arm64/arm64/pmap.c | 19 ++++++++++++++++++-
1 file changed, 18 insertions(+), 1 deletion(-)
diff --git a/sys/arm64/arm64/pmap.c b/sys/arm64/arm64/pmap.c
index 678030f827dd..7d19c927d369 100644
--- a/sys/arm64/arm64/pmap.c
+++ b/sys/arm64/arm64/pmap.c
@@ -290,6 +290,10 @@ VM_PAGE_TO_PV_LIST_LOCK(vm_page_t m)
#define PTE_TO_VM_PAGE(pte) PHYS_TO_VM_PAGE(PTE_TO_PHYS(pte))
#define VM_PAGE_TO_PTE(m) PHYS_TO_PTE(VM_PAGE_TO_PHYS(m))
+static struct mtx cmap_lock;
+static void *cmap1_addr;
+static pt_entry_t *cmap1_pte;
+
/*
* The presence of this flag indicates that the mapping is writeable.
* If the ATTR_S1_AP_RO bit is also set, then the mapping is clean, otherwise
@@ -1363,7 +1367,7 @@ pmap_bootstrap(void)
virtual_avail = preinit_map_va + PMAP_PREINIT_MAPPING_SIZE;
virtual_avail = roundup2(virtual_avail, L1_SIZE);
- virtual_end = VM_MAX_KERNEL_ADDRESS - PMAP_MAPDEV_EARLY_SIZE;
+ virtual_end = VM_MAX_KERNEL_ADDRESS - PMAP_MAPDEV_EARLY_SIZE - L2_SIZE;
kernel_vm_end = virtual_avail;
/*
@@ -1419,6 +1423,19 @@ pmap_bootstrap(void)
alloc_pages(msgbufpv, round_page(msgbufsize) / PAGE_SIZE);
msgbufp = (void *)msgbufpv;
+ /* Allocate space for the CPU0 CMAP */
+ bs_state.va = virtual_end;
+ pmap_bootstrap_l2_table(&bs_state);
+ pmap_store(&bs_state.l3[pmap_l3_index(bs_state.va)],
+ PHYS_TO_PTE(pmap_early_vtophys((vm_offset_t)bs_state.l3)) |
+ ATTR_AF | pmap_sh_attr | ATTR_S1_XN | ATTR_KERN_GP |
+ ATTR_S1_IDX(VM_MEMATTR_WRITE_BACK) | L3_PAGE);
+ dsb(ishst);
+
+ mtx_init(&cmap_lock, "SYSMAPS", NULL, MTX_DEF);
+ cmap1_addr = (void *)(virtual_end + L3_SIZE);
+ cmap1_pte = &bs_state.l3[pmap_l3_index((vm_offset_t)cmap1_addr)];
+
pa = pmap_early_vtophys(bs_state.freemempos);
physmem_exclude_region(start_pa, pa - start_pa, EXFLAG_NOALLOC);
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