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

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Message-ID: <CA+55aFyu-LHqMaZBaa7VNamxhUR99F4Xr+nL9esLDUBhotopVg@mail.gmail.com>
Date:   Thu, 9 Mar 2017 10:15:22 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Kees Cook <keescook@...omium.org>,
        Laura Abbott <labbott@...hat.com>,
        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 Thu, Mar 9, 2017 at 10:10 AM, Linus Torvalds
<torvalds@...ux-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;
        } else
                __supported_pte_mask &= ~_PAGE_GLOBAL;

but maybe there's something wrong with the percpu cr4 caching?

               Linus