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

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Message-ID: <CACT4Y+ar18tcxx0tOthV0JBrmWsLXtXAjXVFX4sac5k1UGJ7Lw@mail.gmail.com>
Date:   Fri, 27 May 2022 19:04:07 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     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 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