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Date: Thu, 09 Mar 2017 19:31:03 +0100
From: Daniel Borkmann <daniel@iogearbox.net>
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To: Linus Torvalds <torvalds@linux-foundation.org>
CC: Thomas Gleixner <tglx@linutronix.de>,
        Kees Cook <keescook@chromium.org>, Laura Abbott <labbott@redhat.com>,
        Ingo Molnar <mingo@kernel.org>, Peter Anvin <hpa@zytor.com>,
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        Network Development <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>, LKP <lkp@01.org>, ast@fb.com,
        the arch/x86 maintainers <x86@kernel.org>,
        "David S. Miller" <davem@davemloft.net>
Subject: Re: [net/bpf] 3051bf36c2 BUG: unable to handle kernel paging request
 at 0000a7cf
References: <20170301125426.l4nf65rx4wahohyl@wfg-t540p.sh.intel.com> <20170302202338.ci6wwb3yzjmdy4n2@wfg-t540p.sh.intel.com> <58B88353.2010508@iogearbox.net> <CA+55aFy97mLPLb4WXmRn-xLMNt+bNkrb_vaBsh+HOMLLnKPv7Q@mail.gmail.com> <58C08535.3070000@iogearbox.net> <CAGXu5jLB_+47FEJYTYJ5u6-u+vOBpWo_0tWuiNKnGmuMjL-mMQ@mail.gmail.com> <7af7bcc9-9115-be9f-2240-a022487e9b70@redhat.com> <CAGXu5jLm3jbJoQAsBsTiiQGK1==JTnSkN_GLsuBGqFvAz5B3AQ@mail.gmail.com> <58C152F1.9090004@iogearbox.net> <alpine.DEB.2.20.1703091409080.3521@nanos> <58C157E6.1010909@iogearbox.net> <alpine.DEB.2.20.1703091547460.3521@nanos> <58C19607.6000605@iogearbox.net> <CA+55aFyxM--wyvxXGhBOqdJHcdC_kKvGYpv-C5SpYvRNkbEmGw@mail.gmail.com> <CA+55aFyu-LHqMaZBaa7VNamxhUR99F4Xr+nL9esLDUBhotopVg@mail.gmail.com>
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On 03/09/2017 07:15 PM, Linus Torvalds wrote:
> On Thu, Mar 9, 2017 at 10:10 AM, Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
>>
>> Very odd. We should always have PGE (0x0080) set in cr4 (if the CPU
>> supports it).
>
> Daniel, do you see the code in probe_page_size_mask() triggering?
>
>          /* Enable PGE if available */
>          if (boot_cpu_has(X86_FEATURE_PGE)) {
>                  cr4_set_bits_and_update_boot(X86_CR4_PGE);
>                  __supported_pte_mask |= _PAGE_GLOBAL;

We do have boot_cpu_has(X86_FEATURE_PGE) and go indeed into this
branch here. So it seems something must be clearing it later, hmm.

>          } else
>                  __supported_pte_mask &= ~_PAGE_GLOBAL;
>
> but maybe there's something wrong with the percpu cr4 caching?
>
>                 Linus
>