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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Daniel Borkmann <daniel@iogearbox.net>
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>,
	Fengguang Wu <fengguang.wu@intel.com>,
	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
Date: Thu, 9 Mar 2017 09:48:20 -0800	[thread overview]
Message-ID: <CA+55aFyxvUx0J=p8jh8N1a80Vt+f6M-rg=L3zxyiv69bOYhkKQ@mail.gmail.com> (raw)
In-Reply-To: <58C16C6A.2060400@iogearbox.net>

On Thu, Mar 9, 2017 at 6:53 AM, Daniel Borkmann <daniel@iogearbox.net> wrote:
>
> Fwiw, I tried switching from using cr4
> (__native_flush_tlb_global_irq_disabled())
> to slower cr3 (__native_flush_tlb()) in "-cpu kvm64" mode, and it looks like
> it also lets all test cases pass (rodata_test, test_setmem, test_bpf), no
> corruption happening, etc.

Ok. I think this is conclusive: the qemu "-cpu kvm64" case is
definitely broken, since changing CR4.PGE is definitely
architecturally defined to flush all TLB entries.

This is not a guest kernel bug.

Of course, the bug may still be in the *host* kernel. Maybe the
emulation does something wrong. I see

        if (((cr4 ^ old_cr4) & pdptr_bits) ||
            (!(cr4 & X86_CR4_PCIDE) && (old_cr4 & X86_CR4_PCIDE)))
                kvm_mmu_reset_context(vcpu);

(where pdptr_bits includes the PGE bit), but I'm not sure if emulation
is supposed to do something else too.

                   Linus

  reply	other threads:[~2017-03-09 17:48 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-03-01 12:54 [net/bpf] 3051bf36c2 BUG: unable to handle kernel paging request at 0000a7cf Fengguang Wu
2017-03-02 20:23 ` Fengguang Wu
2017-03-02 20:40   ` Daniel Borkmann
2017-03-08 19:25     ` Linus Torvalds
2017-03-08 22:27       ` Daniel Borkmann
2017-03-08 22:36         ` Kees Cook
2017-03-08 22:51           ` Daniel Borkmann
2017-03-08 23:55           ` Laura Abbott
2017-03-09  5:36             ` Kees Cook
2017-03-09 13:04               ` Daniel Borkmann
2017-03-09 13:10                 ` Thomas Gleixner
2017-03-09 13:25                   ` Daniel Borkmann
2017-03-09 14:49                     ` Thomas Gleixner
2017-03-09 17:51                       ` Daniel Borkmann
2017-03-09 18:08                         ` David Miller
2017-03-09 18:10                         ` Linus Torvalds
2017-03-09 18:15                           ` Linus Torvalds
2017-03-09 18:31                             ` Daniel Borkmann
2017-03-09 21:32                               ` Daniel Borkmann
2017-03-09 21:55                                 ` Borislav Petkov
2017-03-09 22:07                                   ` Borislav Petkov
2017-03-09 22:11                                     ` Daniel Borkmann
2017-03-09 22:48                                       ` Borislav Petkov
2017-03-09 23:26                                         ` Linus Torvalds
2017-03-09 23:44                                           ` Borislav Petkov
2017-03-10  0:13                                             ` Daniel Borkmann
2017-03-12 21:40                                           ` Borislav Petkov
2017-03-09 14:53                     ` Daniel Borkmann
2017-03-09 17:48                       ` Linus Torvalds [this message]
2017-03-08 22:43         ` Linus Torvalds
2017-03-09  1:34           ` Fengguang Wu
2017-03-09 13:09       ` Thomas Gleixner

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