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From:   Michael Ellerman <mpe@ellerman.id.au>
To:     Christophe Leroy <christophe.leroy@c-s.fr>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>
Cc:     linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH] powerpc/8xx: Fix permanently mapped IMMR region.
In-Reply-To: <ad9d45119a48a92bf122781d0c79c9407baa12d7.1566554026.git.christophe.leroy@c-s.fr>
References: <ad9d45119a48a92bf122781d0c79c9407baa12d7.1566554026.git.christophe.leroy@c-s.fr>
Date:   Mon, 18 Nov 2019 22:17:46 +1100
Message-ID: <87sgmlcu1x.fsf@mpe.ellerman.id.au>
MIME-Version: 1.0
Content-Type: text/plain
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Christophe Leroy <christophe.leroy@c-s.fr> writes:
> When not using large TLBs, the IMMR region is still
> mapped as a whole block in the FIXMAP area.
>
> Do not remove pages mapped in the FIXMAP region when
> initialising paging.
>
> Properly report that the IMMR region is block-mapped even
> when not using large TLBs.
>
> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
> ---
>  arch/powerpc/mm/mem.c        |  8 --------
>  arch/powerpc/mm/nohash/8xx.c | 13 +++++++------
>  2 files changed, 7 insertions(+), 14 deletions(-)

This blows up pmac32_defconfig + qemu mac99 for me with:

  NET: Registered protocol family 1
  RPC: Registered named UNIX socket transport module.
  RPC: Registered udp transport module.
  RPC: Registered tcp transport module.
  RPC: Registered tcp NFSv4.1 backchannel transport module.
  PCI: CLS 0 bytes, default 32
  Trying to unpack rootfs image as initramfs...
  BUG: Unable to handle kernel data access on write at 0xfffdf000
  Faulting instruction address: 0xc001eb4c
  Oops: Kernel access of bad area, sig: 11 [#1]
  BE PAGE_SIZE=4K MMU=Hash PowerMac
  Modules linked in:
  CPU: 0 PID: 1 Comm: swapper Not tainted 5.4.0-rc2-gcc49+ #50
  NIP:  c001eb4c LR: c0394214 CTR: 00000080
  REGS: ef0b5a70 TRAP: 0300   Not tainted  (5.4.0-rc2-gcc49+)
  MSR:  00009032 <EE,ME,IR,DR,RI>  CR: 44088444  XER: 20000000
  DAR: fffdf000 DSISR: 42000000 
  GPR00: 00000080 ef0b5b28 ef0b0000 fffdf000 ef2001e4 00000000 fffdeffc fffe0000 
  GPR08: ef2011e8 00000008 00000009 00000004 28088442 00000000 c0005734 00000000 
  GPR16: 00000000 00000000 00000000 00000000 c07f0000 c0735600 00000000 ef09f500 
  GPR24: fffdf000 00000000 00000000 00000000 fffdf000 ef0b5c38 00001000 00001000 
  NIP [c001eb4c] memcpy+0x88/0x10c
  LR [c0394214] iov_iter_copy_from_user_atomic+0x1fc/0x468
  Call Trace:
  [ef0b5b28] [c0394060] iov_iter_copy_from_user_atomic+0x48/0x468 (unreliable)
  [ef0b5b68] [c0131438] generic_perform_write+0xfc/0x218
  [ef0b5bb8] [c01360bc] __generic_file_write_iter+0x134/0x26c
  [ef0b5bf8] [c0136324] generic_file_write_iter+0x130/0x1d8
  [ef0b5c28] [c01a1754] __vfs_write+0x170/0x220
  [ef0b5ca8] [c01a34f0] vfs_write+0xcc/0x1e0
  [ef0b5cd8] [c01a386c] ksys_write+0xd0/0x120
  [ef0b5d08] [c08a03a4] xwrite+0x44/0xa4
  [ef0b5d28] [c08a0b64] do_copy+0x94/0xdc
  [ef0b5d48] [c08a0044] write_buffer+0x40/0x68
  [ef0b5d68] [c08a00cc] flush_buffer+0x60/0xe4
  [ef0b5d98] [c08e87bc] __gunzip+0x2f0/0x3d0
  [ef0b5dd8] [c08a0974] unpack_to_rootfs+0x1d8/0x334
  [ef0b5e38] [c08a1238] populate_rootfs+0x80/0x168
  [ef0b5e68] [c0005494] do_one_initcall+0x58/0x1f4
  [ef0b5ed8] [c089e918] kernel_init_freeable+0x198/0x29c
  [ef0b5f18] [c000574c] kernel_init+0x18/0x110
  [ef0b5f38] [c0016274] ret_from_kernel_thread+0x14/0x1c
  Instruction dump:
  4200fff0 5400f0bf 7c0903a6 41820010 85240004 95260004 4200fff8 54a0d97f 
  54a506fe 39600004 7c0903a6 4182004c <7c0b37ec> 80e40004 81040008 8124000c 
  ---[ end trace 52276ec2410ac084 ]---


cheers