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

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Date:   Fri, 27 May 2022 19:12:41 +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 19:04, Dmitry Vyukov <dvyukov@...gle.com> 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



Is CONFIG_CMDLINE broken on riscv?
I am running with:

CONFIG_CMDLINE="earlyprintk=serial net.ifnames=0
sysctl.kernel.hung_task_all_cpu_backtrace=1 ima_policy=tcb
nf-conntrack-ftp.ports=20000 nf-conntrack-tftp.ports=20000
nf-conntrack-sip.ports=20000 nf-conntrack-irc.ports=20000
nf-conntrack-sane.ports=20000 binder.debug_mask=0
rcupdate.rcu_expedited=1 no_hash_pointers page_owner=on
sysctl.vm.nr_hugepages=4 sysctl.vm.nr_overcommit_hugepages=4
secretmem.enable=1 sysctl.max_rcu_stall_to_panic=1
msr.allow_writes=off dummy_hcd.num=2 smp.csd_lock_timeout=300000
watchdog_thresh=165 workqueue.watchdog_thresh=420
sysctl.net.core.netdev_unregister_timeout_secs=420 panic_on_warn=1"

But getting BUGs with the default timeout:
watchdog: BUG: soft lockup - CPU#0 stuck for 23s! [kworker/0:4:2039]