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Subject: Re: [GIT PULL] x86/topology changes for v5.3
From:   Xi Ruoyao <xry111@mengyan1223.wang>
To:     Jiri Kosina <jikos@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Kees Cook <keescook@chromium.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Ingo Molnar <mingo@kernel.org>,
        Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
        Borislav Petkov <bp@alien8.de>, Len Brown <lenb@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
        Tony Luck <tony.luck@intel.com>,
        Bob Moore <robert.moore@intel.com>,
        Erik Schmauss <erik.schmauss@intel.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Daniel Bristot de Oliveira <bristot@redhat.com>
Date:   Wed, 10 Jul 2019 21:31:35 +0800
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On 2019-07-10 15:28 +0200, Jiri Kosina wrote:
> On Wed, 10 Jul 2019, Jiri Kosina wrote:

> > > > > BUG: unable to handle page fault for address: ffffffff9edc1598
> > > > > #PF: supervisor write access in kernel mode
> > > > > #PF: error_code(0x0003) - permissions violation

> > Hm, and it seems to explode on dereferencing the static_key* in %rsi
> 
> 								  ^^^ %rdi of
> course
> 
> >   21:   48 8b 37                mov    (%rdi),%rsi
> >   24:   83 e6 03                and    $0x3,%esi
> >   27:   48 09 c6                or     %rax,%rsi
> >   2a:*  48 89 37                mov    %rsi,(%rdi)              <-- trapping
> > instruction
> > 
> > which looks odd, as it derefenced it successfully just 3 instructions ago.

It seems the MMU (I guess ?) allows to read it, but disallows to write it:
"supervisor write access in kernel mode".
-- 
Xi Ruoyao <xry111@mengyan1223.wang>
School of Aerospace Science and Technology, Xidian University