powerpc/fixmap: Fix VM debug warning on unmap
Unmapping a fixmap entry is done by calling __set_fixmap()
with FIXMAP_PAGE_CLEAR as flags.
Today, powerpc __set_fixmap() calls map_kernel_page().
map_kernel_page() is not happy when called a second time
for the same page.
WARNING: CPU: 0 PID: 1 at arch/powerpc/mm/pgtable.c:194 set_pte_at+0xc/0x1e8
CPU: 0 PID: 1 Comm: swapper Not tainted
5.16.0-rc3-s3k-dev-01993-g350ff07feb7d-dirty #682
NIP:
c0017cd4 LR:
c00187f0 CTR:
00000010
REGS:
e1011d50 TRAP: 0700 Not tainted (
5.16.0-rc3-s3k-dev-01993-g350ff07feb7d-dirty)
MSR:
00029032 <EE,ME,IR,DR,RI> CR:
42000208 XER:
00000000
GPR00:
c0165fec e1011e10 c14c0000 c0ee2550 ff800000 c0f3d000 00000000 c001686c
GPR08:
00001000 b00045a9 00000001 c0f58460 c0f50000 00000000 c0007e10 00000000
GPR16:
00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
GPR24:
00000000 00000000 c0ee2550 00000000 c0f57000 00000ff8 00000000 ff800000
NIP [
c0017cd4] set_pte_at+0xc/0x1e8
LR [
c00187f0] map_kernel_page+0x9c/0x100
Call Trace:
[
e1011e10] [
c0736c68] vsnprintf+0x358/0x6c8 (unreliable)
[
e1011e30] [
c0165fec] __set_fixmap+0x30/0x44
[
e1011e40] [
c0c13bdc] early_iounmap+0x11c/0x170
[
e1011e70] [
c0c06cb0] ioremap_legacy_serial_console+0x88/0xc0
[
e1011e90] [
c0c03634] do_one_initcall+0x80/0x178
[
e1011ef0] [
c0c0385c] kernel_init_freeable+0xb4/0x250
[
e1011f20] [
c0007e34] kernel_init+0x24/0x140
[
e1011f30] [
c0016268] ret_from_kernel_thread+0x5c/0x64
Instruction dump:
7fe3fb78 48019689 80010014 7c630034 83e1000c 5463d97e 7c0803a6 38210010
4e800020 81250000 712a0001 41820008 <
0fe00000>
9421ffe0 93e1001c 48000030
Implement unmap_kernel_page() which clears an existing pte.
Reported-by: Maxime Bizon <mbizon@freebox.fr>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Tested-by: Maxime Bizon <mbizon@freebox.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/b0b752f6f6ecc60653e873f385c6f0dce4e9ab6a.1638789098.git.christophe.leroy@csgroup.eu
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