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Message-ID: <87mtoxendq.fsf@mpe.ellerman.id.au>
Date: Tue, 31 Aug 2021 23:48:17 +1000
From: Michael Ellerman <mpe@...erman.id.au>
To: Christophe Leroy <christophe.leroy@...roup.eu>,
Nathan Chancellor <nathan@...nel.org>
Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Paul Mackerras <paulus@...ba.org>,
linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v4 4/4] powerpc/ptdump: Convert powerpc to GENERIC_PTDUMP
Christophe Leroy <christophe.leroy@...roup.eu> writes:
> Le 30/08/2021 à 13:55, Michael Ellerman a écrit :
>> Christophe Leroy <christophe.leroy@...roup.eu> writes:
>>> Le 30/08/2021 à 09:52, Michael Ellerman a écrit :
>>>> Christophe Leroy <christophe.leroy@...roup.eu> writes:
>>>>> Le 29/08/2021 à 20:55, Nathan Chancellor a écrit :
>>>>>> On Thu, Jul 08, 2021 at 04:49:43PM +0000, Christophe Leroy wrote:
>>>>>>> This patch converts powerpc to the generic PTDUMP implementation.
>>>>>>>
>>>>>>
>>>>>> This patch as commit e084728393a5 ("powerpc/ptdump: Convert powerpc to
>>>>>> GENERIC_PTDUMP") in powerpc/next causes a panic with Fedora's ppc64le
>>>>>> config [1] when booting up in QEMU with [2]:
>>>>>>
>>>>>> [ 1.621864] BUG: Unable to handle kernel data access on read at 0xc0eeff7f00000000
>>>>>> [ 1.623058] Faulting instruction address: 0xc00000000045e5fc
>>>>>> [ 1.623832] Oops: Kernel access of bad area, sig: 11 [#1]
>>>>>> [ 1.624318] LE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=2048 NUMA PowerNV
>>>>>> [ 1.625015] Modules linked in:
>>>>>> [ 1.625463] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.14.0-rc7-next-20210827 #16
>>>>>> [ 1.626237] NIP: c00000000045e5fc LR: c00000000045e580 CTR: c000000000518220
>>>>>> [ 1.626839] REGS: c00000000752b820 TRAP: 0380 Not tainted (5.14.0-rc7-next-20210827)
>>>>>> [ 1.627528] MSR: 9000000002009033 <SF,HV,VEC,EE,ME,IR,DR,RI,LE> CR: 84002482 XER: 20000000
>>>>>> [ 1.628449] CFAR: c000000000518300 IRQMASK: 0
>>>>>> [ 1.628449] GPR00: c00000000045e580 c00000000752bac0 c0000000028a9300 0000000000000000
>>>>>> [ 1.628449] GPR04: c200800000000000 ffffffffffffffff 000000000000000a 0000000000000001
>>>>>> [ 1.628449] GPR08: c0eeff7f00000000 0000000000000012 0000000000000000 0000000000000000
>>>>>> [ 1.628449] GPR12: 0000000000000000 c000000002b20000 fffffffffffffffe c000000002971a70
>>>>>> [ 1.628449] GPR16: c000000002960040 c0000000011a8f98 c00000000752bbf0 ffffffffffffffff
>>>>>> [ 1.628449] GPR20: c2008fffffffffff c0eeff7f00000000 c000000002971a68 c00a0003ff000000
>>>>>> [ 1.628449] GPR24: c000000002971a78 0000000000000002 0000000000000001 c0000000011a8f98
>>>>>> [ 1.628449] GPR28: c0000000011a8f98 c0000000028daef8 c200800000000000 c200900000000000
>>>>>> [ 1.634090] NIP [c00000000045e5fc] __walk_page_range+0x2bc/0xce0
>>>>>> [ 1.635117] LR [c00000000045e580] __walk_page_range+0x240/0xce0
>>>>>> [ 1.635755] Call Trace:
>>>>>> [ 1.636018] [c00000000752bac0] [c00000000045e580] __walk_page_range+0x240/0xce0 (unreliable)
>>>>>> [ 1.636811] [c00000000752bbd0] [c00000000045f234] walk_page_range_novma+0x74/0xb0
>>>>>> [ 1.637459] [c00000000752bc20] [c000000000518448] ptdump_walk_pgd+0x98/0x170
>>>>>> [ 1.638138] [c00000000752bc70] [c0000000000aa988] ptdump_check_wx+0x88/0xd0
>>>>>> [ 1.638738] [c00000000752bd50] [c00000000008d6d8] mark_rodata_ro+0x48/0x80
>>>>>> [ 1.639299] [c00000000752bdb0] [c000000000012a34] kernel_init+0x74/0x1a0
>>>>>> [ 1.639842] [c00000000752be10] [c00000000000cfd4] ret_from_kernel_thread+0x5c/0x64
>>>>>> [ 1.640597] Instruction dump:
>>>>>> [ 1.641021] 38e7ffff 39490010 7ce707b4 7fca5436 79081564 7d4a3838 7908f082 794a1f24
>>>>>> [ 1.641740] 78a8f00e 30e6ffff 7ea85214 7ce73110 <7d48502a> 78f90fa4 2c2a0000 39290010
>>>>>> [ 1.642771] ---[ end trace 6cf72b085097ad52 ]---
>>>>>> [ 1.643220]
>>>>>> [ 2.644228] Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b
>>>>>> [ 2.645523] ---[ end Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b ]---
>>>>>>
>>>>>> This is not compiler specific, I can reproduce it with GCC 11.2.0 and
>>>>>> binutils 2.37. If there is any additional information I can provide,
>>>>>> please let me know.
>>>>>
>>>>> Can you provide a dissassembly of __walk_page_range() ? Or provide your vmlinux binary.
>>>>
>>>> It seems to be walking of the end of the pgd.
>>>>
>>>> [ 3.373800] walk_p4d_range: addr c00fff0000000000 end c00fff8000000000
>>>> [ 3.373852] walk_p4d_range: addr c00fff8000000000 end c010000000000000 <- end of pgd at PAGE_OFFSET + 4PB
>>>> [ 3.373905] walk_p4d_range: addr c010000000000000 end c010008000000000
>>>
>>> Yes, I want it to walk from TASK_SIZE_MAX up to 0xffffffffffffffff :)
>>
>> But the page table doesn't span that far? 0_o
>>
>>> static struct ptdump_range ptdump_range[] __ro_after_init = {
>>> {TASK_SIZE_MAX, ~0UL},
>>> {0, 0}
>>> };
>>>
>>> Ok, well, ppc32 go up to 0xffffffff
>>>
>>> What's the top address to be used for ppc64 ?
>>
>> It's different for (hash | radix) x page size.
>>
>> The below works, and matches what we used to do.
>>
>> Possibly we can come up with something cleaner, not sure.
>>
>> cheers
>>
>>
>> diff --git a/arch/powerpc/mm/ptdump/ptdump.c b/arch/powerpc/mm/ptdump/ptdump.c
>> index 2d80d775d15e..3d3778a74969 100644
>> --- a/arch/powerpc/mm/ptdump/ptdump.c
>> +++ b/arch/powerpc/mm/ptdump/ptdump.c
>> @@ -359,6 +359,8 @@ static int __init ptdump_init(void)
>> ptdump_range[0].start = KERN_VIRT_START;
>> else
>> ptdump_range[0].start = PAGE_OFFSET;
>> +
>> + ptdump_range[0].end = ptdump_range[0].start + (PGDIR_SIZE * PTRS_PER_PGD);
>
> Hum ...
>
> It was:
>
> for (i = pgd_index(addr); i < PTRS_PER_PGD; i++, pgd++, addr += PGDIR_SIZE) {
>
> And there is
>
> #define pgd_index(a) (((a) >> PGDIR_SHIFT) & (PTRS_PER_PGD - 1))
Yes you're right.
> Do we have the following ?
>
> pgd_index(KERN_VIRT_START) == 0
No.
Since 0034d395f89d ("powerpc/mm/hash64: Map all the kernel regions in the same 0xc range")
It's:
pgd_index(PAGE_OFFSET) == 0
> Shouldn't it be something like
>
> ptdump_range[0].end = PAGE_OFFSET + (PGDIR_SIZE * PTRS_PER_PGD);
Yep.
And we should also change the start address for hash to be PAGE_OFFSET.
Even though we don't expect anything in the page tables between
PAGE_OFFSET and KERN_VIRT_START, it's still good to check that range.
cheers
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