linux-kernel - Re: [syzbot] riscv/fixes test error: lost connection to test machine

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Message-ID: <fcb6d1aa-78bb-cfad-7655-cbab59f8d5c3@ghiti.fr>
Date:   Sat, 28 May 2022 10:03:23 +0200
From:   Alexandre Ghiti <alex@...ti.fr>
To:     Dmitry Vyukov <dvyukov@...gle.com>,
        Alexandre Ghiti <alexandre.ghiti@...onical.com>
Cc:     syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        syzbot <syzbot+2c5da6a0a16a0c4f34aa@...kaller.appspotmail.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>
Subject: Re: [syzbot] riscv/fixes test error: lost connection to test machine

On 5/27/22 19:04, Dmitry Vyukov wrote:
> On Fri, 27 May 2022 at 16:01, Alexandre Ghiti
> <alexandre.ghiti@...onical.com> wrote:
>> On Friday, May 27, 2022 at 3:55:24 PM UTC+2 Dmitry Vyukov wrote:
>>> On Fri, 27 May 2022 at 15:50, Alexandre Ghiti
>>> <alexand...@...onical.com> wrote:
>>>> On Friday, May 27, 2022 at 3:02:01 PM UTC+2 Dmitry Vyukov wrote:
>>>>> On Fri, 27 May 2022 at 14:55, syzbot
>>>>> <syzbot+2c5da6...@...kaller.appspotmail.com> wrote:
>>>>>> Hello,
>>>>>>
>>>>>> syzbot found the following issue on:
>>>>>>
>>>>>> HEAD commit: c932edeaf6d6 riscv: dts: microchip: fix gpio1 reg property..
>>>>>> git tree: git://git.kernel.org/pub/scm/linux/kernel/git/riscv/linux.git fixes
>>>>>> console output: https://syzkaller.appspot.com/x/log.txt?x=1418add5f00000
>>>>>> kernel config: https://syzkaller.appspot.com/x/.config?x=aa6b5702bdf14a17
>>>>>> dashboard link: https://syzkaller.appspot.com/bug?extid=2c5da6a0a16a0c4f34aa
>>>>>> compiler: riscv64-linux-gnu-gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
>>>>>> userspace arch: riscv64
>>>>>>
>>>>>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
>>>>>> Reported-by: syzbot+2c5da6...@...kaller.appspotmail.com
>>>>> The CONFIG_KASAN_VMALLOC allows riscv kernel to boot, but now Go
>>>>> processes started crashing with:
>>>>>
>>>>> 1970/01/01 00:06:55 fuzzer started
>>>>> runtime: lfstack.push invalid packing: node=0xffffff5908a940 cnt=0x1
>>>>> packed=0xffff5908a9400001 -> node=0xffff5908a940
>>>>> fatal error: lfstack.push
>>>>> runtime stack:
>>>>> runtime.throw({0x30884c, 0xc})
>>>>> /usr/local/go/src/runtime/panic.go:1198 +0x60
>>>>> runtime.(*lfstack).push(0xdb3850, 0xffffff5908a940)
>>>>> /usr/local/go/src/runtime/lfstack.go:30 +0x1a8
>>>>>
>>>>> Go runtime tries to shove some data into the upper 16 bits of pointers
>>>>> assuming they are unused.
>>>>> However, the original pointer node=0xffffff5908a940 suggest riscv now
>>>>> has 56-bit users-space address space?
>>>>
>>>> Yes, sv57 was merged recently.
>>>>
>>>>> Documentation/riscv/vm-layout.rst claims 48-bit pointers:
>>>>> "
>>>>> The RISC-V privileged architecture document states that the 64bit addresses
>>>>> "must have bits 63–48 all equal to bit 47, or else a page-fault exception will
>>>>> occur.":
>>>>
>>>> Thanks for pointing that, I extracted that from the specification before sv57 was specified, I'll fix that.
>>>>
>>>> The current kernel code will use sv57 as it is supported and advertised by qemu, and to my knowledge, you can't downgrade to sv48 unless by re-compiling qemu using the following:
>>>>
>>>> diff --git a/target/riscv/csr.c b/target/riscv/csr.c
>>>> index 6dbe9b541f..a64b50ed75 100644
>>>> --- a/target/riscv/csr.c
>>>> +++ b/target/riscv/csr.c
>>>> @@ -637,7 +637,7 @@ static const char valid_vm_1_10_64[16] = {
>>>> [VM_1_10_MBARE] = 1,
>>>> [VM_1_10_SV39] = 1,
>>>> [VM_1_10_SV48] = 1,
>>>> - [VM_1_10_SV57] = 1
>>>> + [VM_1_10_SV57] = 0
>>>> };
>>>>
>>>> /* Machine Information Registers */
>>>>
>>>>> ...
>>>>> 0000000000000000 | 0 | 0000003fffffffff | 256 GB |
>>>>> user-space virtual memory, different per mm
>>>>> "
>>> There is no kernel config to force SV48/39, right?
>>
>> No, we rely on what the hardware advertises, if it supports sv57, we'll go for sv57, if not, we'll try sv48...etc. I had some patches to force the downgrade by using the device tree but they never got merged though.
> +original CC list
>
> FTR sent Go runtime change to support SV57:
> https://go-review.googlesource.com/c/go/+/409055

Thank you for that, I'll pull that into Ubuntu when merged. Do you know 
if any other programming language does the same and would need a fix too?

>
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> linux-riscv@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv

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