Subject: Re: [PATCH v2 00/15] powerpc/32s: Use BATs/LTLBs for STRICT_KERNEL_RWX

From: Jonathan Neuschäfer <[email-masked]>
Date: Thu, 17 Jan 2019 00:48:16 +0100

On Wed, Jan 16, 2019 at 02:34:53PM +0100, Christophe Leroy wrote:
> Le 16/01/2019 à 14:16, Jonathan Neuschäfer a écrit :
> > On Wed, Jan 16, 2019 at 07:55:29AM +0100, Christophe Leroy wrote:
> > > Le 16/01/2019 à 01:35, Jonathan Neuschäfer a écrit :
> > > > Thinning the kernel down a bit actually makes it boot again. Ooops...!
> > > > Maybe enabling CONFIG_STRICT_KERNEL_RWX has made it just large enough to
> > > > fail the hash table allocation, but there may have been other factors
> > > > involved (I'm not sure exactly).  Sorry for the confusion!
> > > 
> > > Ok, that must be the reason. Thanks for testing.
> > > 
> > > What about the following modification which maps a second 256Mb BAT, does it
> > > helps ?
> > > 
> > > 
> > > 
> > > diff --git a/arch/powerpc/kernel/head_32.S b/arch/powerpc/kernel/head_32.S
> > > index c2f564690778..ea574596de37 100644
> > > --- a/arch/powerpc/kernel/head_32.S
> > > +++ b/arch/powerpc/kernel/head_32.S
> > > @@ -1160,6 +1160,14 @@ initial_bats:
> > >   	mtspr	SPRN_DBAT0U,r11		/* bit in upper BAT register */
> > >   	mtspr	SPRN_IBAT0L,r8
> > >   	mtspr	SPRN_IBAT0U,r11
> > > +#ifdef CONFIG_WII
> > > +	addis	r11,r11,0x10000000@h
> > > +	addis	r8,r8,0x10000000@h
> > > +	mtspr	SPRN_DBAT2L,r8
> > > +	mtspr	SPRN_DBAT2U,r11
> > > +	mtspr	SPRN_IBAT2L,r8
> > > +	mtspr	SPRN_IBAT2U,r11
> > > +#endif
> > >   	isync
> > >   	blr
> > > 
> > > diff --git a/arch/powerpc/mm/ppc_mmu_32.c b/arch/powerpc/mm/ppc_mmu_32.c
> > > index 3f4193201ee7..a334fd5210a8 100644
> > > --- a/arch/powerpc/mm/ppc_mmu_32.c
> > > +++ b/arch/powerpc/mm/ppc_mmu_32.c
> > > @@ -259,6 +259,8 @@ void setup_initial_memory_limit(phys_addr_t
> > > first_memblock_base,
> > >   	/* 601 can only access 16MB at the moment */
> > >   	if (PVR_VER(mfspr(SPRN_PVR)) == 1)
> > >   		memblock_set_current_limit(min_t(u64, first_memblock_size, 0x01000000));
> > > +	else if (IS_ENABLED(CONFIG_WII))
> > > +		memblock_set_current_limit(min_t(u64, first_memblock_size, 0x20000000));
> > >   	else /* Anything else has 256M mapped */
> > >   		memblock_set_current_limit(min_t(u64, first_memblock_size, 0x10000000));
> > >   }
> > 
> > I haven't tested it, but this patch won't be enough, because we're only
> > looking at the first memblock, and the additional memory in the Wii
> > (MEM2) is the second memblock.
> > 
> 
> Yes right.
> 
> 
> Would the following work instead ?
> 
> memblock_set_current_limit(0x20000000);

With the config at https://gist.githubusercontent.com/neuschaefer/12ccc87ff8aeff543fad558e8742cd2b/raw/d49d321709cac364779e6893bbd91ff5a80bcb03/config
it still doesn't boot, but with a different error:

top of MEM2 @ 13F00000

zImage starting: loaded at 0x01000000 (sp: 0x0178afa0)
Allocating 0x166b2c8 bytes for kernel...
Decompressing (0x00000000 <- 0x01011000:0x01788799)...
Done! Decompressed 0xf421f4 bytes

Linux/PowerPC load: root=/dev/mmcblk0p2 rootwait console=usbgecko1
Finalizing device tree... flat tree at 0x178b7a0
[    0.000000] printk: bootconsole [udbg0] enabled
[    0.000000] __memblock_find_range_top_down(1000:20000000, 100000:100000, ffffffff, 0)
[    0.000000] __memblock_find_range_top_down: in loop, 10000000:13f00000
[    0.000000] Total memory = 319MB; using 1024kB for hash table (at d3e00000)
[    0.000000] __memblock_find_range_top_down(1000:20000000, 1000:1000, ffffffff, 0)
[    0.000000] __memblock_find_range_top_down: in loop, 10000000:13e00000
[    0.000000] __memblock_find_range_top_down(1000:20000000, 1000:1000, ffffffff, 0)
[    0.000000] __memblock_find_range_top_down: in loop, 10000000:13dff000
[    0.000000] BUG: Unable to handle kernel data access at 0xc106a434
[    0.000000] Faulting instruction address: 0xc0071bf4
[    0.000000] Oops: Kernel access of bad area, sig: 11 [#1]
[    0.000000] BE PREEMPT
[    0.000000] Modules linked in:
[    0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 5.0.0-rc1-wii-00038-gc34b70d591b6-dirty #1337
[    0.000000] NIP:  c0071bf4 LR: c00727d8 CTR: 00000000
[    0.000000] REGS: c0f1fd30 TRAP: 0300   Not tainted  (5.0.0-rc1-wii-00038-gc34b70d591b6-dirty)
[    0.000000] MSR:  00001032 <ME,IR,DR,RI>  CR: 44002842  XER: 00000000
[    0.000000] DAR: c106a434 DSISR: 40000000
[    0.000000] GPR00: c0074a98 c0f1fde0 c0ead4a0 c0ead4a0 c0ead9c8 00000008 00000000 00000000
[    0.000000] GPR08: 00000003 c106a418 00000258 00000001 24000444 fb43ef5b c0f30000 7561f327
[    0.000000] GPR16: c0f40000 691cfd11 38afe359 f161e513 00000000 c0ead9c8 00000001 00000000
[    0.000000] GPR24: 00000000 c0f46288 00000000 c0ead4a0 c0ead9c8 00000008 c0ead4a0 00000100
[    0.000000] NIP [c0071bf4] mark_lock+0x64/0x858
[    0.000000] LR [c00727d8] __lock_acquire+0x334/0x1a40
[    0.000000] Call Trace:
[    0.000000] [c0f1fe20] [00000006] 0x6
[    0.000000] [c0f1fed0] [c0074a98] lock_acquire+0x110/0x20c
[    0.000000] [c0f1ff10] [c085e8cc] _raw_spin_lock+0x44/0x60
[    0.000000] [c0f1ff30] [c007f220] vprintk_emit+0xa0/0x328
[    0.000000] [c0f1ff70] [c007fc48] printk+0x5c/0x84
[    0.000000] [c0f1ffb0] [c0c00854] start_kernel+0x64/0x460
[    0.000000] [c0f1fff0] [00003438] 0x3438
[    0.000000] Instruction dump:
[    0.000000] 41820170 55086cfe 550a083c 7d4a4214 554a1838 3d20c0f4 7d4a4214 39296288
[    0.000000] 554a1838 3d290012 7d295214 39293f38 <8129001c> 7fe94839 41820028 3bc00001
[    0.000000] random: get_random_bytes called from print_oops_end_marker+0x34/0x6c with crng_init=0
[    0.000000] ---[ end trace 0000000000000000 ]---
[    0.000000]
[    0.000000] Kernel panic - not syncing: Attempted to kill the idle task!

Not sure what's wrong. It does work with wii_defconfig, though.
I think for now I'm happy without this patch, as it doesn't seem to be
really necessary.

Jonathan