Crash on FSL Book3E due to pte_pgprot()? (was Re: [PATCH v3 12/24] powerpc/mm: use pte helpers in generic code)

[Michael Ellerman]

Christophe Leroy <christophe.leroy@xxxxxx> writes:

> Get rid of platform specific _PAGE_XXXX in powerpc common code and
> use helpers instead.
>
> mm/dump_linuxpagetables.c will be handled separately
>
> Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>
> Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxx>
> ---
>  arch/powerpc/include/asm/book3s/32/pgtable.h |  9 +++------
>  arch/powerpc/include/asm/nohash/32/pgtable.h | 12 ++++++++----
>  arch/powerpc/include/asm/nohash/pgtable.h    |  3 +--
>  arch/powerpc/mm/pgtable.c                    | 21 +++++++--------------
>  arch/powerpc/mm/pgtable_32.c                 | 15 ++++++++-------
>  arch/powerpc/mm/pgtable_64.c                 | 14 +++++++-------
>  arch/powerpc/xmon/xmon.c                     | 12 +++++++-----
>  7 files changed, 41 insertions(+), 45 deletions(-)

So turns out this patch *also* breaks my p5020ds :)

Even with patch 4 merged, see next.

It's the same crash:

  pcieport 2000:00:00.0: AER enabled with IRQ 480
  Unable to handle kernel paging request for data at address 0x8000080080080000
  Faulting instruction address: 0xc0000000000192cc
  Oops: Kernel access of bad area, sig: 11 [#1]
  BE SMP NR_CPUS=24 CoreNet Generic
  Modules linked in:
  CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.19.0-rc3-gcc7x-g98c847323b3a #1
  NIP:  c0000000000192cc LR: c0000000005d0f9c CTR: 0000000000100000
  REGS: c0000000f31bb400 TRAP: 0300   Not tainted  (4.19.0-rc3-gcc7x-g98c847323b3a)
  MSR:  0000000080029000 <CE,EE,ME>  CR: 24000224  XER: 00000000
  DEAR: 8000080080080000 ESR: 0000000000800000 IRQMASK: 0 
  GPR00: c0000000005d0f84 c0000000f31bb688 c00000000117dc00 8000080080080000 
  GPR04: 0000000000000000 0000000000400000 00000ffbff241010 c0000000f31b8000 
  GPR08: 0000000000000000 0000000000100000 0000000000000000 c0000000012d4710 
  GPR12: 0000000084000422 c0000000012ff000 c000000000002774 0000000000000000 
  GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 
  GPR20: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 
  GPR24: 0000000000000000 0000000000000000 8000080080080000 c0000000ffff89a8 
  GPR28: c0000000f3576400 c0000000f3576410 0000000000400000 c0000000012ecc98 
  NIP [c0000000000192cc] ._memset_io+0x6c/0x9c
  LR [c0000000005d0f9c] .fsl_qman_probe+0x198/0x928
  Call Trace:
  [c0000000f31bb688] [c0000000005d0f84] .fsl_qman_probe+0x180/0x928 (unreliable)
  [c0000000f31bb728] [c0000000006432ec] .platform_drv_probe+0x60/0xb4
  [c0000000f31bb7a8] [c00000000064083c] .really_probe+0x294/0x35c
  [c0000000f31bb848] [c000000000640d2c] .__driver_attach+0x148/0x14c
  [c0000000f31bb8d8] [c00000000063d7dc] .bus_for_each_dev+0xb0/0x118
  [c0000000f31bb988] [c00000000063ff28] .driver_attach+0x34/0x4c
  [c0000000f31bba08] [c00000000063f648] .bus_add_driver+0x174/0x2bc
  [c0000000f31bbaa8] [c0000000006418bc] .driver_register+0x90/0x180
  [c0000000f31bbb28] [c000000000643270] .__platform_driver_register+0x60/0x7c
  [c0000000f31bbba8] [c000000000ee2a70] .fsl_qman_driver_init+0x24/0x38
  [c0000000f31bbc18] [c0000000000023fc] .do_one_initcall+0x64/0x2b8
  [c0000000f31bbcf8] [c000000000e9f480] .kernel_init_freeable+0x3a8/0x494
  [c0000000f31bbda8] [c000000000002798] .kernel_init+0x24/0x148
  [c0000000f31bbe28] [c0000000000009e8] .ret_from_kernel_thread+0x58/0x70
  Instruction dump:
  4e800020 2ba50003 40dd003c 3925fffc 5488402e 7929f082 7d082378 39290001 
  550a801e 7d2903a6 7d4a4378 794a0020 <91430000> 38630004 4200fff8 70a50003 


Comparing a working vs broken kernel, it seems to boil down to the fact
that we're filtering out more PTE bits now that we use pte_pgprot() in
ioremap_prot().

With the old code we get:
  ioremap_prot: addr 0xff800000 flags 0x241215
  ioremap_prot: addr 0xff800000 flags 0x241215
  map_kernel_page: ea 0x8000080080080000 pa 0xff800000 pte 0xff800241215


And now we get:
  ioremap_prot: addr 0xff800000 flags 0x241215 pte 0x241215
  ioremap_prot: addr 0xff800000 pte 0x241215
  ioremap_prot: addr 0xff800000 prot 0x241014
  map_kernel_page: ea 0x8000080080080000 pa 0xff800000 pte 0xff800241014

So we're losing 0x201, which for nohash book3e is:

  #define _PAGE_PRESENT	0x000001 /* software: pte contains a translation */
  #define _PAGE_PSIZE_4K	0x000200


I haven't worked out if it's one or both of those that matter.

The question is what's the right way to fix it? Should pte_pgprot() not
be filtering those bits out on book3e?

cheers