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

From David Miller <davem@davemloft.net>
Newsgroups linux.kernel
Subject Re: [net/bpf] 3051bf36c2 BUG: unable to handle kernel paging request at 0000a7cf
Date 2017-03-09 19:10 +0100
Message-ID <tjaFI-ma-33@gated-at.bofh.it> (permalink)
References <tj6Vr-6eP-3@gated-at.bofh.it> <tj7HQ-6AN-9@gated-at.bofh.it> <tjaw2-8vb-3@gated-at.bofh.it>
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From: Daniel Borkmann <daniel@iogearbox.net>
Date: Thu, 09 Mar 2017 18:51:03 +0100

> I added some debugging around __native_flush_tlb_global_irq_disabled()
> and if I understand it correctly, the idea of cr4 is that we need to
> toggle X86_CR4_PGE in order to trigger a TLB flush.
> 
> What I see is that original cr4 is 0x610. The cpu_tlbstate.cr4 is
> consistent to native_read_cr4() and since cr4 is != 0, it tells me
> based on the comment in native_read_cr4() that cr4 seems to be
> supported. Thus, meaning we end up with writing ...
> 
>   native_write_cr4(0x610);
>   native_write_cr4(0x610);
> 
> ... twice, and this just doesn't trigger the desired TLB flush. I
> changed the code into the following ...
> 
>         cr4 = this_cpu_read(cpu_tlbstate.cr4);
>         /* clear PGE */
> -       native_write_cr4(cr4 & ~X86_CR4_PGE);
> +       native_write_cr4(cr4 ^ X86_CR4_PGE);
>         /* write old PGE again and flush TLBs */
>         native_write_cr4(cr4);
> 
> ... and the test cases seem to be working for me now with "-cpu
> kvm64",
> so that seems to trigger the TLB we were missing.

Great detective work Daniel.

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Thread

Re: [net/bpf] 3051bf36c2 BUG: unable to handle kernel paging request  at 0000a7cf Fengguang Wu <fengguang.wu@intel.com> - 2017-03-02 21:30 +0100
  Re: [net/bpf] 3051bf36c2 BUG: unable to handle kernel paging request  at 0000a7cf Daniel Borkmann <daniel@iogearbox.net> - 2017-03-02 22:40 +0100
    Re: [net/bpf] 3051bf36c2 BUG: unable to handle kernel paging request  at 0000a7cf Linus Torvalds <torvalds@linux-foundation.org> - 2017-03-08 20:30 +0100
      Re: [net/bpf] 3051bf36c2 BUG: unable to handle kernel paging request  at 0000a7cf Kees Cook <keescook@chromium.org> - 2017-03-08 23:40 +0100
        Re: [net/bpf] 3051bf36c2 BUG: unable to handle kernel paging request  at 0000a7cf Daniel Borkmann <daniel@iogearbox.net> - 2017-03-09 00:20 +0100
        Re: [net/bpf] 3051bf36c2 BUG: unable to handle kernel paging request  at 0000a7cf Laura Abbott <labbott@redhat.com> - 2017-03-09 01:30 +0100
          Re: [net/bpf] 3051bf36c2 BUG: unable to handle kernel paging request  at 0000a7cf Kees Cook <keescook@chromium.org> - 2017-03-09 06:40 +0100
            Re: [net/bpf] 3051bf36c2 BUG: unable to handle kernel paging request  at 0000a7cf Daniel Borkmann <daniel@iogearbox.net> - 2017-03-09 14:10 +0100
              Re: [net/bpf] 3051bf36c2 BUG: unable to handle kernel paging request  at 0000a7cf Thomas Gleixner <tglx@linutronix.de> - 2017-03-09 14:20 +0100
                Re: [net/bpf] 3051bf36c2 BUG: unable to handle kernel paging request  at 0000a7cf Daniel Borkmann <daniel@iogearbox.net> - 2017-03-09 15:10 +0100
                Re: [net/bpf] 3051bf36c2 BUG: unable to handle kernel paging request  at 0000a7cf Thomas Gleixner <tglx@linutronix.de> - 2017-03-09 16:00 +0100
                Re: [net/bpf] 3051bf36c2 BUG: unable to handle kernel paging request  at 0000a7cf Daniel Borkmann <daniel@iogearbox.net> - 2017-03-09 19:00 +0100
                Re: [net/bpf] 3051bf36c2 BUG: unable to handle kernel paging  request at 0000a7cf David Miller <davem@davemloft.net> - 2017-03-09 19:10 +0100
                Re: [net/bpf] 3051bf36c2 BUG: unable to handle kernel paging request  at 0000a7cf Linus Torvalds <torvalds@linux-foundation.org> - 2017-03-09 19:20 +0100
                Re: [net/bpf] 3051bf36c2 BUG: unable to handle kernel paging request  at 0000a7cf Linus Torvalds <torvalds@linux-foundation.org> - 2017-03-09 19:20 +0100
                Re: [net/bpf] 3051bf36c2 BUG: unable to handle kernel paging request  at 0000a7cf Daniel Borkmann <daniel@iogearbox.net> - 2017-03-09 19:40 +0100
                Re: [net/bpf] 3051bf36c2 BUG: unable to handle kernel paging request  at 0000a7cf Daniel Borkmann <daniel@iogearbox.net> - 2017-03-09 22:40 +0100
                Re: [net/bpf] 3051bf36c2 BUG: unable to handle kernel paging request  at 0000a7cf Borislav Petkov <bp@suse.de> - 2017-03-09 23:10 +0100
                Re: [net/bpf] 3051bf36c2 BUG: unable to handle kernel paging request  at 0000a7cf Daniel Borkmann <daniel@iogearbox.net> - 2017-03-09 23:20 +0100
                Re: [net/bpf] 3051bf36c2 BUG: unable to handle kernel paging request  at 0000a7cf Borislav Petkov <bp@suse.de> - 2017-03-09 23:50 +0100
                Re: [net/bpf] 3051bf36c2 BUG: unable to handle kernel paging request  at 0000a7cf Linus Torvalds <torvalds@linux-foundation.org> - 2017-03-10 00:30 +0100
                Re: [net/bpf] 3051bf36c2 BUG: unable to handle kernel paging request  at 0000a7cf Borislav Petkov <bp@suse.de> - 2017-03-10 00:50 +0100
                Re: [net/bpf] 3051bf36c2 BUG: unable to handle kernel paging request  at 0000a7cf Daniel Borkmann <daniel@iogearbox.net> - 2017-03-10 01:20 +0100
                Re: [net/bpf] 3051bf36c2 BUG: unable to handle kernel paging request  at 0000a7cf Borislav Petkov <bp@suse.de> - 2017-03-12 22:50 +0100
                Re: [net/bpf] 3051bf36c2 BUG: unable to handle kernel paging request  at 0000a7cf Borislav Petkov <bp@suse.de> - 2017-03-09 23:20 +0100
                Re: [net/bpf] 3051bf36c2 BUG: unable to handle kernel paging request  at 0000a7cf Daniel Borkmann <daniel@iogearbox.net> - 2017-03-09 16:00 +0100
                Re: [net/bpf] 3051bf36c2 BUG: unable to handle kernel paging request  at 0000a7cf Linus Torvalds <torvalds@linux-foundation.org> - 2017-03-09 18:50 +0100
      Re: [net/bpf] 3051bf36c2 BUG: unable to handle kernel paging request  at 0000a7cf Linus Torvalds <torvalds@linux-foundation.org> - 2017-03-08 23:50 +0100
        Re: [net/bpf] 3051bf36c2 BUG: unable to handle kernel paging request  at 0000a7cf Fengguang Wu <fengguang.wu@intel.com> - 2017-03-09 02:40 +0100
      Re: [net/bpf] 3051bf36c2 BUG: unable to handle kernel paging request  at 0000a7cf Thomas Gleixner <tglx@linutronix.de> - 2017-03-09 14:50 +0100

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