Re: [PATCH] powerpc: don't select KFENCE on platform PPC_FSL_BOOK3E
From: Christophe Leroy
Date: Tue Oct 12 2021 - 13:28:32 EST
Le 12/10/2021 à 08:24, Michael Ellerman a écrit :
Liu Shixin <liushixin2@xxxxxxxxxx> writes:
kindly ping.
I was under the impression you were trying to debug why it wasn't
working with Christophe.
The investigation was a bit dormant to be honest since Liu confirmed
that neither KFENCE not DEBUG_PAGEALLOC works.
I now looked at the effort to make it work, and it is not trivial.
At the time being, all linear space is mapped with pinned TLBs and
everything is setup for space 0, with space 1 being used temporarily
when doing heavy changes to space 0.
We can't use standard pages for linear space on space 0 because we need
memory mapped at all time for exceptions (on booke exception run with
MMU on in space 0).
In order to use standard pages, we'd need to reorganise the kernel to
have it run mostly in space 1 (for data at least) where we would map
almost everything with standard pages, and keep pinned TLB to map linear
space on space 0 for TLB miss exceptions. Then we'd do more or less like
book3s/32 and switch back into space 1 into other exceptions prolog.
That could be good to do it as we could maybe have more code in common
with non booke 32 bits, but it is not a trivial job.
So I suggest that for now, we just make KFENCE and DEBUG_PAGEALLOC
unselectable for booke/32 (e500 and 44x).
Christophe
cheers
On 2021/9/24 14:39, Liu Shixin wrote:
On platform PPC_FSL_BOOK3E, all lowmem is managed by tlbcam. That means
we didn't really map the kfence pool with page granularity. Therefore,
if KFENCE is enabled, the system will hit the following panic:
BUG: Kernel NULL pointer dereference on read at 0x00000000
Faulting instruction address: 0xc01de598
Oops: Kernel access of bad area, sig: 11 [#1]
BE PAGE_SIZE=4K SMP NR_CPUS=4 MPC8544 DS
Dumping ftrace buffer:
(ftrace buffer empty)
Modules linked in:
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.12.0-rc3+ #298
NIP: c01de598 LR: c08ae9c4 CTR: 00000000
REGS: c0b4bea0 TRAP: 0300 Not tainted (5.12.0-rc3+)
MSR: 00021000 <CE,ME> CR: 24000228 XER: 20000000
DEAR: 00000000 ESR: 00000000
GPR00: c08ae9c4 c0b4bf60 c0ad64e0 ef720000 00021000 00000000 00000000 00000200
GPR08: c0ad5000 00000000 00000000 00000004 00000000 008fbb30 00000000 00000000
GPR16: 00000000 00000000 00000000 00000000 c0000000 00000000 00000000 00000000
GPR24: c08ca004 c08ca004 c0b6a0e0 c0b60000 c0b58f00 c0850000 c08ca000 ef720000
NIP [c01de598] kfence_protect+0x44/0x6c
LR [c08ae9c4] kfence_init+0xfc/0x2a4
Call Trace:
[c0b4bf60] [efffe160] 0xefffe160 (unreliable)
[c0b4bf70] [c08ae9c4] kfence_init+0xfc/0x2a4
[c0b4bfb0] [c0894d3c] start_kernel+0x3bc/0x574
[c0b4bff0] [c0000470] set_ivor+0x14c/0x188
Instruction dump:
7c0802a6 8109d594 546a653a 90010014 54630026 39200000 7d48502e 2c0a0000
41820010 554a0026 5469b53a 7d295214 <81490000> 38831000 554a003c 91490000
random: get_random_bytes called from print_oops_end_marker+0x40/0x78 with crng_init=0
---[ end trace 0000000000000000 ]---
Signed-off-by: Liu Shixin <liushixin2@xxxxxxxxxx>
---
arch/powerpc/Kconfig | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index d46db0bfb998..cffd57bcb5e4 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -185,7 +185,7 @@ config PPC
select HAVE_ARCH_KASAN if PPC32 && PPC_PAGE_SHIFT <= 14
select HAVE_ARCH_KASAN_VMALLOC if PPC32 && PPC_PAGE_SHIFT <= 14
select HAVE_ARCH_KGDB
- select HAVE_ARCH_KFENCE if PPC32
+ select HAVE_ARCH_KFENCE if PPC32 && !PPC_FSL_BOOK3E
select HAVE_ARCH_MMAP_RND_BITS
select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT
select HAVE_ARCH_NVRAM_OPS