Re: [PATCH] powerpc: don't select KFENCE on platform PPC_FSL_BOOK3E

On 2021/9/24 14:41, Christophe Leroy wrote:

Le 24/09/2021 à 08:39, Liu Shixin a écrit :

quoted

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:

Could you please explain a bit more what the problem is ?

KFENCE has been implemented with the same logic as DEBUG_PAGEALLOC.

DEBUG_PAGEALLOC is enabled on FSL_BOOK3E.

In MMU_setup(), __map_without_ltlbs is set to 1 when KFENCE is enabled.

__map_without_ltlbs should disable the use of tlbcam.


So what's wrong really ?

Does DEBUG_PAGEALLOC work on FSL_BOOK3E ?

Thanks
Christophe

hi Christophe,

In the last e-mail I have said that DEBUG_PAGEALLOC works well on FSL_BOOK3E, that is wrong.
Actually, I add some printed information and find DEBUG_PAGEALLOC Skip all pages.
So neither DEBUG_PAGEALLOC nor kfence is really working.

diff --git a/mm/memory.c b/mm/memory.c
index 25fc46e87214..37fb1b14bc3f 100644
--- a/mm/memory.c
+++ b/mm/memory.c

@@ -2564,8 +2564,10 @@ static int apply_to_pmd_range(struct mm_struct *mm, pud_t *pud,
        }
        do {
                next = pmd_addr_end(addr, end);
-               if (pmd_none(*pmd) && !create)
+               if (pmd_none(*pmd) && !create) {
+                       pr_info("---------pmd_none----------\n");
                        continue;
+               }
                if (WARN_ON_ONCE(pmd_leaf(*pmd)))
                        return -EINVAL;
                if (!pmd_none(*pmd) && WARN_ON_ONCE(pmd_bad(*pmd))) {

quoted

     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 <redacted>
---
  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

.