linux-kernel - Re: [next] arm64: boot failed

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Date:   Thu, 9 Jun 2022 11:44:09 +0800
From:   Kefeng Wang <wangkefeng.wang@...wei.com>
To:     Vasily Averin <vvs@...nvz.org>,
        Naresh Kamboju <naresh.kamboju@...aro.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
CC:     Stephen Rothwell <sfr@...b.auug.org.au>,
        Linux-Next Mailing List <linux-next@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        <regressions@...ts.linux.dev>, <lkft-triage@...ts.linaro.org>,
        linux-mm <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Ard Biesheuvel" <ardb@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Raghuram Thammiraju <raghuram.thammiraju@....com>,
        Mark Brown <broonie@...nel.org>, Will Deacon <will@...nel.org>,
        "Roman Gushchin" <roman.gushchin@...ux.dev>,
        Qian Cai <quic_qiancai@...cinc.com>
Subject: Re: [next] arm64: boot failed - next-20220606


On 2022/6/9 10:49, Vasily Averin wrote:
> Dear ARM developers,
> could you please help me to find the reason of this problem?
Hi,
> mem_cgroup_from_obj():
> ffff80000836cf40:       d503245f        bti     c
> ffff80000836cf44:       d503201f        nop
> ffff80000836cf48:       d503201f        nop
> ffff80000836cf4c:       d503233f        paciasp
> ffff80000836cf50:       d503201f        nop
> ffff80000836cf54:       d2e00021        mov     x1, #0x1000000000000            // #281474976710656
> ffff80000836cf58:       8b010001        add     x1, x0, x1
> ffff80000836cf5c:       b25657e4        mov     x4, #0xfffffc0000000000         // #-4398046511104
> ffff80000836cf60:       d34cfc21        lsr     x1, x1, #12
> ffff80000836cf64:       d37ae421        lsl     x1, x1, #6
> ffff80000836cf68:       8b040022        add     x2, x1, x4
> ffff80000836cf6c:       f9400443        ldr     x3, [x2, #8]
>
> x5 : ffff80000a96f000 x4 : fffffc0000000000 x3 : ffff80000ad5e680
> x2 : fffffe00002bc240 x1 : 00000200002bc240 x0 : ffff80000af09740
>
> x0 = 0xffff80000af09740 is an argument of mem_cgroup_from_obj()
> according to System.map it is init_net
>
> This issue is caused by calling virt_to_page() on address of static variable init_net.
> Arm64 consider that addresses of static variables are not valid virtual addresses.
> On x86_64 the same API works without any problem.
>
> Unfortunately I do not understand the cause of the problem.
> I do not see any bugs in my patch.
> I'm using an existing API, mem_cgroup_from_obj(), to find the memory cgroup used
> to account for the specified object.
> In particular, in the current case, I wanted to get the memory cgroup of the
> specified network namespace by the name taken from for_each_net().
> The first object in this list is the static structure unit_net

root@...t:~# cat /proc/kallsyms |grep -w _data
ffff80000a110000 D _data
root@...t:~# cat /proc/kallsyms |grep -w _end
ffff80000a500000 B _end
root@...t:~# cat /proc/kallsyms |grep -w init_net
ffff80000a4eb980 B init_net

the init_net is located in data section, on arm64, it is allowed by 
vmalloc, see

     map_kernel_segment(pgdp, _data, _end, PAGE_KERNEL, &vmlinux_data, 
0, 0);

and the arm has same behavior.

We could let init_net be allocated dynamically, but I think it could 
change a lot.

Any better sugguestion, Catalin?