Following OOPS is encountered while loading test_bpf module
on powerpc 8xx:
[ 218.835567] BUG: Unable to handle kernel data access on write at 0xcb000000
[ 218.842473] Faulting instruction address: 0xc0017a80
[ 218.847451] Oops: Kernel access of bad area, sig: 11 [#1]
[ 218.852854] BE PAGE_SIZE=16K PREEMPT CMPC885
[ 218.857207] SAF3000 DIE NOTIFICATION
[ 218.860713] Modules linked in: test_bpf(+) test_module
[ 218.865867] CPU: 0 UID: 0 PID: 527 Comm: insmod Not tainted
6.11.0-s3k-dev-09856-g3de3d71ae2e6-dirty #1280
[ 218.875546] Hardware name: MIAE 8xx 0x500000 CMPC885
[ 218.880521] NIP: c0017a80 LR: beab859c CTR: 000101d4
[ 218.885584] REGS: cac2bc90 TRAP: 0300 Not tainted
(6.11.0-s3k-dev-09856-g3de3d71ae2e6-dirty)
[ 218.894308] MSR: 00009032 <EE,ME,IR,DR,RI> CR: 55005555 XER: a0007100
[ 218.901290] DAR: cb000000 DSISR: c2000000
[ 218.901290] GPR00: 000185d1 cac2bd50 c21b9580 caf7c030 c3883fcc 00000008
cafffffc 00000000
[ 218.901290] GPR08: 00040000 18300000 20000000 00000004 99005555 100d815e
ca669d08 00000369
[ 218.901290] GPR16: ca730000 00000000 ca2c004c 00000000 00000000 0000035d
00000311 00000369
[ 218.901290] GPR24: ca732240 00000001 00030ba3 c3800000 00000000 00185d48
caf7c000 ca2c004c
[ 218.941087] NIP [c0017a80] memcpy+0x88/0xec
[ 218.945277] LR [beab859c] test_bpf_init+0x22c/0x3c90 [test_bpf]
[ 218.951476] Call Trace:
[ 218.953916] [cac2bd50] [beab8570] test_bpf_init+0x200/0x3c90 [test_bpf]
(unreliable)
[ 218.962034] [cac2bde0] [c0004c04] do_one_initcall+0x4c/0x1fc
[ 218.967706] [cac2be40] [c00a2ec4] do_init_module+0x68/0x360
[ 218.973292] [cac2be60] [c00a5194] init_module_from_file+0x8c/0xc0
[ 218.979401] [cac2bed0] [c00a5568] sys_finit_module+0x250/0x3f0
[ 218.985248] [cac2bf20] [c000e390] system_call_exception+0x8c/0x15c
[ 218.991444] [cac2bf30] [c00120a8] ret_from_syscall+0x0/0x28
This happens in the main loop of memcpy()
==> c0017a80: 7c 0b 37 ec dcbz r11,r6
c0017a84: 80 e4 00 04 lwz r7,4(r4)
c0017a88: 81 04 00 08 lwz r8,8(r4)
c0017a8c: 81 24 00 0c lwz r9,12(r4)
c0017a90: 85 44 00 10 lwzu r10,16(r4)
c0017a94: 90 e6 00 04 stw r7,4(r6)
c0017a98: 91 06 00 08 stw r8,8(r6)
c0017a9c: 91 26 00 0c stw r9,12(r6)
c0017aa0: 95 46 00 10 stwu r10,16(r6)
c0017aa4: 42 00 ff dc bdnz c0017a80 <memcpy+0x88>
Commit ac9f97ff8b32 ("powerpc/8xx: Inconditionally use task PGDIR in
DTLB misses") relies on re-reading DAR register to know if an error is
due to a missing copy of a PMD entry in task's PGDIR, allthough DAR
was already read in the exception prolog and copied into thread
struct. This is because is it done very early in the exception and
there are not enough registers available to keep a pointer to thread
struct.
However, dcbz instruction is buggy and doesn't update DAR register on
fault. That is detected and generates a call to FixupDAR workaround
which updates DAR copy in thread struct but doesn't fix DAR register.
Let's fix DAR in addition to the update of DAR copy in thread struct.
Fixes: ac9f97ff8b32 ("powerpc/8xx: Inconditionally use task PGDIR in DTLB
misses")
Signed-off-by: Christophe Leroy <christophe.le...@csgroup.eu>
---
arch/powerpc/kernel/head_8xx.S | 1 +
1 file changed, 1 insertion(+)
diff --git a/arch/powerpc/kernel/head_8xx.S b/arch/powerpc/kernel/head_8xx.S
index 8120273c7249..78942fd6b4b9 100644
--- a/arch/powerpc/kernel/head_8xx.S
+++ b/arch/powerpc/kernel/head_8xx.S
@@ -495,6 +495,7 @@ FixupDAR:/* Entry point for dcbx workaround. */
bctr /* jump into table */
152:
mfdar r11
+ mtdar r10
mtctr r11 /* restore ctr reg from DAR */
mfspr r11, SPRN_SPRG_THREAD
stw r10, DAR(r11)
--
2.44.0
