netdev - Re: [net/bpf] 3051bf36c2 BUG: unable to handle kernel paging request at 0000a7cf

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Message-ID: <58C157E6.1010909@iogearbox.net>
Date:   Thu, 09 Mar 2017 14:25:58 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Thomas Gleixner <tglx@...utronix.de>
CC:     Kees Cook <keescook@...omium.org>,
        Laura Abbott <labbott@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>, Peter Anvin <hpa@...or.com>,
        Fengguang Wu <fengguang.wu@...el.com>,
        Network Development <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, LKP <lkp@...org>,
        ast@...com, the arch/x86 maintainers <x86@...nel.org>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [net/bpf] 3051bf36c2 BUG: unable to handle kernel paging request
 at 0000a7cf

On 03/09/2017 02:10 PM, Thomas Gleixner wrote:
> On Thu, 9 Mar 2017, Daniel Borkmann wrote:
>> With regard to CPA_FLUSHTLB that Linus mentioned, when I investigated
>> code paths in change_page_attr_set_clr(), I did see that CPA_FLUSHTLB
>> was set each time we switched attrs and a cpa_flush_range() was
>> performed (with the correct number of pages and cache set to 0). That
>> would be a __flush_tlb_all() eventually.
>>
>> Hmm, it indeed might seem likely that this could be an emulation bug.
>
> Which variant of __flush_tlb_all() is used when the test fails?
>
> Check for the following flags in /proc/cpuinfo: pge invpcid

I added the following and booted with both variants:

printk("X86_FEATURE_PGE:%u\n",     static_cpu_has(X86_FEATURE_PGE));
printk("X86_FEATURE_INVPCID:%u\n", static_cpu_has(X86_FEATURE_INVPCID));

"-cpu host" gives:

[    8.326117] X86_FEATURE_PGE:1
[    8.326381] X86_FEATURE_INVPCID:1

"-cpu kvm64" gives:

[    8.517069] X86_FEATURE_PGE:1
[    8.517393] X86_FEATURE_INVPCID:0

Thanks,
Daniel