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05b042a194
When two recent commits that increased the size of the 'struct cpu_entry_area'
were merged in -tip, the 32-bit defconfig build started failing on the following
build time assert:
./include/linux/compiler.h:391:38: error: call to ‘__compiletime_assert_189’ declared with attribute error: BUILD_BUG_ON failed: CPU_ENTRY_AREA_PAGES * PAGE_SIZE < CPU_ENTRY_AREA_MAP_SIZE
arch/x86/mm/cpu_entry_area.c:189:2: note: in expansion of macro ‘BUILD_BUG_ON’
In function ‘setup_cpu_entry_area_ptes’,
Which corresponds to the following build time assert:
BUILD_BUG_ON(CPU_ENTRY_AREA_PAGES * PAGE_SIZE < CPU_ENTRY_AREA_MAP_SIZE);
The purpose of this assert is to sanity check the fixed-value definition of
CPU_ENTRY_AREA_PAGES arch/x86/include/asm/pgtable_32_types.h:
#define CPU_ENTRY_AREA_PAGES (NR_CPUS * 41)
The '41' is supposed to match sizeof(struct cpu_entry_area)/PAGE_SIZE, which value
we didn't want to define in such a low level header, because it would cause
dependency hell.
Every time the size of cpu_entry_area is changed, we have to adjust CPU_ENTRY_AREA_PAGES
accordingly - and this assert is checking that constraint.
But the assert is both imprecise and buggy, primarily because it doesn't
include the single readonly IDT page that is mapped at CPU_ENTRY_AREA_BASE
(which begins at a PMD boundary).
This bug was hidden by the fact that by accident CPU_ENTRY_AREA_PAGES is defined
too large upstream (v5.4-rc8):
#define CPU_ENTRY_AREA_PAGES (NR_CPUS * 40)
While 'struct cpu_entry_area' is 155648 bytes, or 38 pages. So we had two extra
pages, which hid the bug.
The following commit (not yet upstream) increased the size to 40 pages:
x86/iopl: ("Restrict iopl() permission scope")
... but increased CPU_ENTRY_AREA_PAGES only 41 - i.e. shortening the gap
to just 1 extra page.
Then another not-yet-upstream commit changed the size again:
|
||
|---|---|---|
| .. | ||
| amdtopology.c | ||
| cpu_entry_area.c | ||
| debug_pagetables.c | ||
| dump_pagetables.c | ||
| extable.c | ||
| fault.c | ||
| highmem_32.c | ||
| hugetlbpage.c | ||
| ident_map.c | ||
| init.c | ||
| init_32.c | ||
| init_64.c | ||
| iomap_32.c | ||
| ioremap.c | ||
| kasan_init_64.c | ||
| kaslr.c | ||
| kmmio.c | ||
| Makefile | ||
| mem_encrypt.c | ||
| mem_encrypt_boot.S | ||
| mem_encrypt_identity.c | ||
| mm_internal.h | ||
| mmap.c | ||
| mmio-mod.c | ||
| mpx.c | ||
| numa.c | ||
| numa_32.c | ||
| numa_64.c | ||
| numa_emulation.c | ||
| numa_internal.h | ||
| pageattr-test.c | ||
| pageattr.c | ||
| pat.c | ||
| pat_internal.h | ||
| pat_rbtree.c | ||
| pf_in.c | ||
| pf_in.h | ||
| pgtable.c | ||
| pgtable_32.c | ||
| physaddr.c | ||
| physaddr.h | ||
| pkeys.c | ||
| pti.c | ||
| setup_nx.c | ||
| srat.c | ||
| testmmiotrace.c | ||
| tlb.c | ||